Why aren't the two greatest commandments part of the Decalogue?

#Abstraction allows 1 function() to contain {tasks} in order to run / execute multiple functions at once. - In Matthew 22:36-40, Jesus (Yeshua, ישׁוּעָ) of Nazareth is using Abstraction to simplify our Father's Commandments / Mitsvot (מִצְו‍ֹת) into two main functions which help us maintain the covenant law.

#Abstraction-1. Deuteronomy 6:5 [MT] :

[5] "And you shall love YHVH, your-God, with all your heart and with all your soul, and with all your means. (וְאָ֣הַבְתָּ֔ אֵ֖ת יְהֹוָ֣ה אֱלֹהֶ֑יךָ בְּכָל־לְבָֽבְךָ֥ וּבְכָל־נַפְשְׁךָ֖ וּבְכָל־מְאֹדֶֽךָ) "

• //Deuteronomy 6:5 [MT] executes { Exodus20:3-11 }

#Abstraction-2. Leviticus 19:18 [MT] :

"And you-shall-love your-neighbor as-yourself" ( וְאָֽהַבְתָּ֥ לְרֵֽעֲךָ֖ כָּמ֑וֹךָ )

• //Leviticus 19:18 [MT] executes { Exodus 20:12-14 }

The Decalogue was intended to be the starting point of the Israelites' journey. As they continued in obedience, they would eventually discern the principles that underlay them, and in the process come to something like true righteousness.

Imagine if the tablets carried down by Moses had simply given these two greatest commandments. The commandments are not specific. They leave an enormous amount of wiggle-room for people who want to obey the letter of the law while ignoring the spirit entirely. That would have been an enormous problem because we human beings are very, very skilled at kidding ourselves. Even today people say and do many things I cannot find even suggested in the Scriptures, and call it service to God because they are doing it in the meeting house instead of their living room, and have taken the notion that they love God.

This was already a problem with the Israelites; they didn't entirely abandon the worship of Yahweh, they simply went in for the idolatrous worship as well. "Yes, I love Yahweh, but I also love that rocking party going down at the Asherah pole." Imagine if there was nothing that directly reined in the greed, lust, and pride to which they are already prone?

Those of us who are parents even experience this. We make our children obey household rules long before they understand why the rules are needed. To delay the what until they understand the why would result in complete failure.

So the reason for the absence of the greater commandments from the Decalogue is that you have to obey the lesser commandments before the greater ones can be understood.

I would say the 2 greatest commandments are indirectly part of the 10 commandments.

36 “Teacher, which is the greatest commandment in the Law?” 37 Jesus replied: “‘Love the Lord your God with all your heart and with all your soul and with all your mind.’

Commands 1-4 - relating to God

3 “You shall have no other gods before Me. 4 “You shall not make for yourself an idol, or any likeness of what is in heaven above or on the earth beneath or in the water under the earth. 5 You shall not worship them or serve them; for I, the Lord your God, am a jealous God, visiting the iniquity of the fathers on the children, on the third and the fourth generations of those who hate Me, 6 but showing lovingkindness to thousands, to those who love Me and keep My commandments. 7 “You shall not take the name of the Lord your God in vain, for the Lord will not leave him unpunished who takes His name in vain. 8 “Remember the sabbath day, to keep it holy. 9 Six days you shall labor and do all your work, 10 but the seventh day is a sabbath of the Lord your God; in it you shall not do any work, you or your son or your daughter, your male or your female servant or your cattle or your sojourner who stays with you. 11 For in six days the Lord made the heavens and the earth, the sea and all that is in them, and rested on the seventh day; therefore the Lord blessed the sabbath day and made it holy.

38 This is the first and greatest commandment. 39 And the second is like it: ‘Love your neighbor as yourself.’ 40 All the Law and the Prophets hang on these two commandments.”

Commands 6-10 - relating to others

12 “Honor your father and your mother, that your days may be prolonged in the land which the Lord your God gives you. 13 “You shall not murder. 14 “You shall not commit adultery. 15 “You shall not steal. 16 “You shall not bear false witness against your neighbor. 17 “You shall not covet your neighbor’s house; you shall not covet your neighbor’s wife or his male servant or his female servant or his ox or his donkey or anything that belongs to your neighbor.”

Why aren't the two greatest commandments part of the Decalogue?

There are a few reasons for this.

The words of Jesus are a summary of the Decalogue.

Man needs moral rules to be broken down, so he is capable of knowing what is the difference between right and wrong. In this regards, a summary or the Decalogue just does not do that.

Secondly, it was God’s intention, to have his only Begotten Son explain the the meaning of the Decalogue in as way that exemplifies his wisdom in front of the Pharisees.

The Scriptures show us on more than one occasion that Our Lord astonished the Jewish community with his knowledge, learning and miracles:

The Rejection at Nazareth

…2When the Sabbath came, He began to teach in the synagogue, and many who heard Him were astonished. “Where did this man get these ideas?” they asked. “What is this wisdom He has been given? And how can He perform such miracles? 3Isn’t this the carpenter, the son of Mary and the brother of James, Joses, Judas, and Simon? Aren’t His sisters here with us as well? And they took offense at Him. 4Then Jesus said to them, “Only in his hometown, among his relatives, and in his own household is a prophet without honor.”… - Mark 6:3

God the Father desired his Divine Son to be the one to truly enlighten all of mankind.

But the Pharisees, hearing that he had silenced the Sadducees, came together. - Matthew 22:34

But the Pharisees hearing. The theological attack. The Pharisees had been overcome in their political assault, but seeing the admiration of the multitude for the answers of Jesus, they feel bound to destroy our Lord’s authority by confounding him in public. “Silenced,” according to the Greek text, might be rendered “muzzled” [cf. Deut. 25:4; 1 Cor. 9:9; 1 Tim. 5:18]. “The Pharisees … came together” in order to deliberate about their course of action [cf. Ps. 2:2]; the result of this council is given in the words “and one of them”; for they agreed to depute a delegate instead of approaching Jesus in a body. “A doctor of the law” occurs only here in the first gospel, while the third gospel employs the term more frequently; etymologically considered, the Greek word for “doctor of the law” denotes one learned in the law, while “scribe” denotes one versed in Scripture. Hence some think that the scribes explained the law in the synagogues, while the doctors explained it in the schools and in private assemblies, or that the scribes explained matters of doctrine, while the doctors taught matters of practice [cf. Calmet], or that the scribes explained the Haggada, while the doctors were concerned with the Halacha [cf. Schanz]; but since the Scripture and the law were practically identical for the Jews [cf. Jn. 10:37; 15:25; 7:49; 12:34; 1 Cor. 14:21], the doctors of the law must have been identical with those learned in the Scriptures, a conclusion that is confirmed by Mk. 12:28, where the “doctor of the law” is called “one of the scribes,” and also by Lk. 11:52, 53, where the two titles are indiscriminately applied to the same class of persons [cf. Knabenbauer].

And one of them, a doctor of the law, asked him, tempting him: Master, which is the great commandment in the law? - Mathew 22:35-36

“Tempting him” appears to contradict the second gospel [Mk. 12:32, 33], in which the scribe seems to have been sincere in his question; the discrepancy cannot be explained by contending that the Pharisees acted hypocritically, while their representative was fully sincere [cf. Paschasius, Sylveira, Schanz], nor by maintaining that the questioner tempted Jesus in a good sense, as the queen of Saba had tempted Solomon [cf. 1 Kings 10:1; Lam. Augustine De cons. evang. ii. 73, 141; Lapide], for both these explanations do violence to the text of St. Matthew. The scribe may have come with an evil intention, and may have been changed or perhaps wholly converted after the answer of Jesus [cf. Chrysostom, Augustine, Theophylact, Euthymius, Paschasius, Thomas Aquinas, Dionysius, Salmeron Sylveira]. The Jewish doctors enumerated 613 commandments [cf. Surenhusius, p. iv. p. 291], 248 of which were positive [equal to the number of bones in the human body], and 365 negative [equal to the number of days in the year]. These commandments were distinguished into great and small ones [cf. Schöttgen, Wünsche, Wetstein, ad v. 19], but practically it was hard to decide whether a given precept was great or small. The Greek text admits a double interpretation: first, what kind of commandment is a great one in the law, a question inquiring after the criterion according to which a great commandment might be distinguished from a small one [cf. Arnoldi, Schegg, Bisping, Schanz, Meyer, Weiss]; secondly, which particular precept is the greatest in the law, an interpretation favored by our Lord’s answer and the parallel text of the second gospel [Mk. 12:28]. Both points were much disputed among the Jewish doctors, so that Jesus could not answer the question in either sense without incurring the odium of some of the doctors.

Jesus said to him: Thou shalt love the Lord thy God with thy whole heart and with thy whole soul and with thy whole mind. This is the greatest and the first commandment. - Matthew 22:37-38

Jesus escapes the snare by drawing attention to the great principles of morality, instead of entering into the Rabbinic discussions on the ceremonial law; for no Jewish doctors could under any circumstances have denied the paramount importance of the moral obligations that were the soul of all external observances. The law which Jesus cites is taken from Deut. 6:5; according to the first gospel we read “with thy whole mind” instead of the original “with thy whole strength,” while Mk. 12:30 and Lk. 10:27 combine the expressions of Deut. and St. Matthew, reading “with thy whole mind, and with thy whole strength,” and “with all thy strength, and with all thy mind.” The verb “love” in both Greek and Latin text denotes the love of esteem rather than the love of affection. The manner of love described by the evangelists has found various explanations: first, the single clauses express different faculties or parts of man, but nearly every commentator of note has his own manner of explaining them [cf. Origen, Opus Imperfectum, Thomas Aquinas, Theophylact, Alb. Dionysius, Cajetan, Salmeron, Sylveira]; secondly, the “heart” denotes our will, the “soul” the lower faculties, the “mind” our whole way of thinking and willing, so that we must love God with our whole will, and with our lower faculties, and in both ways we must love him completely or with all our strength [cf. Augustine De doctr. christ. i. 22; Opus Imperfectum, Salmeron, Jansenius, Knabenbauer]; thirdly, the different clauses only indicate that our love for God must be supreme, i. e. that we must not adhere to anything contrary to God, that God alone must be our last end, that he must be our greatest good in appreciation at least [cf. Maldonado, Lapide, Jansenius c. 81, comment. in concord. evang.].

And the second is like to this: Thou shalt love thy neighbour as thyself. On these two commandments dependeth the whole law and the prophets. - Matthew 22: 39-40

“And the second” commandment in dignity as well as in width “is like to this”; because man must be loved as being the image of God [Origen, Opus Imperfectum, Alb. Thomas Aquinas, Faber Stapulensis, Dionysius], so that the love of our neighbor extends as far as the likeness of God extends [cf. Tostatus quæst. 278, in c. xxii.; Sylveira]. “Thou shalt love thy neighbor as thyself” requires first, that we must love the neighbor for the same motive for which we love ourselves; secondly, that we must wish our neighbor the same kind of good we desire for ourselves [cf. Augustine De vera relig. xlvi. 87; Maldonado, Mt. 7:12]. Then Jesus adds the reason why the two foregoing precepts are the greatest: “On these two commandments dependeth” [cf. Is. 22:23–25] “the whole law and the prophets,” i. e. the whole moral law; for these two laws contain all other moral laws [cf. Theophylact, Rabanus, St Bruno], they are the end of all other laws [cf. 1 Tim. 1:5; Rom. 3:19; Alb. Thomas Aquinas, Cajetan], they are the motives for the observance of all the other laws [cf. Dionysius, Lapide], and they give the form to all morally good actions [cf. Rom. 13:10; Alb. Thomas Aquinas, Cajetan].

Jesus had a way of calling attention to that which underpinned the Law as the Jews were accustomed to viewing it. For instance:

“You have heard that it was said to those of old, ‘You shall not murder; and whoever murders will be liable to judgment.’ But I say to you that everyone who is angry with his brother will be liable to judgment; whoever insults his brother will be liable to the council; and whoever says, ‘You fool!’ will be liable to the hell of fire. - Matthew 5:21-22

The letter (of the Law/Old Covenant) kills but the spirit (of the Law/New Covenant) gives life:

Not that we are sufficient in ourselves to claim anything as coming from us, but our sufficiency is from God, who has made us sufficient to be ministers of a new covenant, not of the letter but of the Spirit. For the letter kills, but the Spirit gives life. - 2 Corinthians 3:5-6

The first and greatest commandment, "Love the Lord your God with all your heart and with all your soul and with all your mind", summarizes the Spirit of the first 4 commandments of the Decalogue in particular and, since all sin is against God, all 10 in general. If a person truly loves God with everything that they have they will not be in violation of the first 4 commands which specifically have one's personal relationship with God in view.

The second commandment, "Love your neighbor as yourself", summarizes the Spirit of the last 6 commandments in particular. These commands have to do with one's personal relationship and responsibility under God to our fellow man. If a person loves God in the fashion that produces righteousness under the first 4 commands they will be able, then, to love neighbors as self and not be in violation of the remaining 6 commands.

Some view the 5th command within the first grouping (vertical relationship), others as within the second grouping (horizontal relationship), and still others as a kind of a hinge between the two. Regardless of where #5 falls, love for God is critical for it's fulfillment.

In this way all the Law and the Prophets hang on these two. Thus it is said in 1 John 4:19-21 -

We love because he first loved us. If anyone says, “I love God,” and hates his brother, he is a liar; for he who does not love his brother whom he has seen cannot love God whom he has not seen. And this commandment we have from him: whoever loves God must also love his brother.

The only way to love our neighbor as ourselves (2nd greatest command) is to first love God with all we have (1st greatest command). The only way to love God in this fashion is to receive the love that God first loved us with:

In this is love, not that we have loved God but that he loved us and sent his Son to be the propitiation for our sins. - 1 John 4:10

The way to receive this love of God is to believe in the Son, to be born again/from above (John 3) and to be indwelt by the Holy Spirit, through whom the love of God is shed abroad in the heart's of men:

Therefore, since we have been justified by faith, we have peace with God through our Lord Jesus Christ. Through him we have also obtained access by faith into this grace in which we stand, and we rejoice in hope of the glory of God. Not only that, but we rejoice in our sufferings, knowing that suffering produces endurance, and endurance produces character, and character produces hope, and hope does not put us to shame, because God's love has been poured into our hearts through the Holy Spirit who has been given to us. - Romans 5:1-5

Therefore:

There is therefore now no condemnation for those who are in Christ Jesus. For the law of the Spirit of life has set you free in Christ Jesus from the law of sin and death. For God has done what the law, weakened by the flesh, could not do. By sending his own Son in the likeness of sinful flesh and for sin, he condemned sin in the flesh, in order that the righteous requirement of the law might be fulfilled in us, who walk not according to the flesh but according to the Spirit. - Romans 8:1-4