Why does the apostle John write far more clearly about the deity of Christ than seems to be the case in the other gospel accounts?

If we accept that John wrote his gospel about 30 years after the other three, that is, near the end of the first century, then it would appear that the Gospel of John was written to counter the rise of the two great heresies that have plagued the church throughout its history, namely:

• Gnosticism - Jesus was not really human but only appeared to be human - only those in "the know" (hence the name) realize this
• Arianism - Jesus was not fully divine but only human

The Gospel of John emphasizes Jesus' divinity AND his humanity as do his epistles.

The assumption that John wrote clearly about the deity of Christ, but the other three gospels don't, doesn't really hold up under similarities shown below.

We know some have questioned John because of the Passover day/date differences, but not for this reason. Nonetheless, is the assumption accurate?

Matthew

Matthew opens with Christ's genealogy. 23 verses into chapter 1, he states "God is with us".

Behold, a virgin shall be with child, and shall bring forth a son, and they shall call his name Emmanuel, which being interpreted is, God with us. Matthew 1:23

He further states they came to worship him. Worship is reserved for God alone.

Saying, Where is he that is born King of the Jews? for we have seen his star in the east, and are come to worship him. Matthew 2:2

Throughout Matthew, he quotes fulfilled prophecy, for example Psalm 2:7.

And lo a voice from heaven, saying, This is my beloved Son, in whom I am well pleased. Matthew 3:17

Mark

He opens with the account of Christ's baptism, quoting Isaiah 44:3.

For I will pour water upon him that is thirsty, and floods upon the dry ground: I will pour my spirit upon thy seed, and my blessing upon thine offspring:

The "I" pronoun refers to the previous verse.

Thus saith the LORD that made thee, and formed thee from the womb, which will help thee; Fear not, O Jacob, my servant; and thou, Jesurun, whom I have chosen.

It is God who will pour out His Spirit. Thus John the Baptist understood.

I indeed have baptized you with water: but he shall baptize you with the Holy Ghost. Mark 1:8

Who heals? How did devils know Christ?

And he healed many that were sick of divers diseases, and cast out many devils; and suffered not the devils to speak, because they knew him.

The climax is that only God forgives sins.

When Jesus saw their faith, he said unto the sick of the palsy, Son, thy sins be forgiven thee. ... Why doth this man thus speak blasphemies? who can forgive sins but God only? Mark 2:5, 7

Luke

Luke opens with the terms of the forerunner (John the Baptist), then segues into Christ.

He shall be great, and shall be called the Son of the Highest: and the Lord God shall give unto him the throne of his father David: Luke 1:32

Luke is referencing a prophecy from Isaiah.

For unto us a child is born, unto us a son is given: and the government shall be upon his shoulder: and his name shall be called Wonderful, Counsellor, The mighty God, The everlasting Father, The Prince of Peace. Of the increase of his government and peace there shall be no end, upon the throne of David, and upon his kingdom, to order it, and to establish it with judgment and with justice from henceforth even for ever. The zeal of the LORD of hosts will perform this. Isaiah 9:6-7

Called the mighty God (el, same as Emmanuel- God with us). It doesn't get much clearer than that.

John

With those things in mind, John's first verses are an explosion of Good News, yet a reiteration.

In the beginning was the Word, and the Word was with God, and the Word was God. John 1:1, Matthew 1:23 quoted above

And the Word was made flesh, and dwelt among us, (and we beheld his glory, the glory as of the only begotten of the Father,) full of grace and truth. John 1:14, Luke 1:31 quoted above

The next day John seeth Jesus coming unto him, and saith, Behold the Lamb of God, which taketh away the sin of the world. John 1:29, Mark 2:5 quoted above

Conclusion

It appears that John wrote clearly, but it also appears that the other three gospel accounts also wrote clearly. As Irenaeus noted some 1,800 years ago, it is impossible for the gospels to be less or more than four each with a combined purpose.

8. It is not possible that the Gospels can be either more or fewer in number than they are. For, since there are four zones of the world in which we live, and four principal winds,3449 while the Church is scattered throughout all the world, and the “pillar and ground”3450 of the Church is the Gospel and the spirit of life; it is fitting that she should have four pillars, breathing out immortality on every side, and vivifying men afresh. From which fact, it is evident that the Word, the Artificer of all, He that sitteth upon the cherubim, and contains all things, He who was manifested to men, has given us the Gospel under four aspects, but bound together by one Spirit. As also David says, when entreating His manifestation, “Thou that sittest between the cherubim, shine forth.”3451 For the cherubim, too, were four-faced, and their faces were images of the dispensation of the Son of God. For, [as the Scripture] says, “The first living creature was like a lion,”3452 symbolizing His effectual working, His leadership, and royal power; the second [living creature] was like a calf, signifying [His] sacrificial and sacerdotal order; but “the third had, as it were, the face as of a man,”—an evident description of His advent as a human being; “the fourth was like a flying eagle,” pointing out the gift of the Spirit hovering with His wings over the Church. And therefore the Gospels are in accord with these things, among which Christ Jesus is seated. For that according to John relates His original, effectual, and glorious generation from the Father, thus declaring, “In the beginning was the Word, and the Word was with God, and the Word was God.”3453 Also, “all things were made by Him, and without Him was nothing made.” For this reason, too, is that Gospel full of all confidence, for such is His person.3454 But that according to Luke, taking up [His] priestly character, commenced with Zacharias the priest offering sacrifice to God. For now was made ready the fatted calf, about to be immolated for3455 the finding again of the younger son. Matthew, again, relates His generation as a man, saying, “The book of the generation of Jesus Christ, the son of David, the son of Abraham;”3456 and also, “The birth of Jesus Christ was on this wise.” This, then, is the Gospel of His humanity;3457 for which reason it is, too, that [the character of] a humble and meek man is kept up through the whole Gospel. Mark, on the other hand, commences with [a reference to] the prophetical spirit coming down from on high to men, saying, “The beginning of the Gospel of Jesus Christ, as it is written in Esaias the prophet,”—pointing to the winged aspect of the Gospel; and on this account he made a compendious and cursory narrative, for such is the prophetical character. And the Word of God Himself used to converse with the ante-Mosaic patriarchs, in accordance with His divinity 429 and glory; but for those under the law he instituted a sacerdotal and liturgical service.3458 Afterwards, being made man for us, He sent the gift of the celestial Spirit over all the earth, protecting us with His wings. Such, then, as was the course followed by the Son of God, so was also the form of the living creatures; and such as was the form of the living creatures, so was also the character of the Gospel.3459 For the living creatures are quadriform, and the Gospel is quadriform, as is also the course followed by the Lord. For this reason were four principal (καθολικαί) covenants given to the human race:3460 one, prior to the deluge, under Adam; the second, that after the deluge, under Noah; the third, the giving of the law, under Moses; the fourth, that which renovates man, and sums up all things in itself by means of the Gospel, raising and bearing men upon its wings into the heavenly kingdom. Irenaeus, AH III, XI, 8

The gospel of John was written at a time when the belief that Christ was God who became human (incarnation) was already common/universal in the church as evident in the earliest New Testament record found in Paul's epistles (cf. Philippians 2:6-7, 1 Cor 8:6, 10:4 Gal. 1:1, 1:12, 4:4). Paul wrote his epistles with high divine Christology circa 40-50 whilst John wrote his gospel circa 90-100.

The Synoptic gospels did have Christ as God incarnate.

• Matthew spoke of the one who was born of the virgin as "God with us" (Greek: Ο Θεος, just like what John 20:28 had) and who actually was "always with us".

• Mark had Jesus as the "son of God" who forgive sins when "God alone forgive sins" (Mark 2:7). Here the term son of God did not merely imply human Davidic ancestry/kingship of Jesus but his unique relationship with the Father, with whom he shares the same identity as "Κυριος" ( Lord = God in the Jewish sense).

• Luke had Jesus as a pre-existent divine being (a divine Spirit, not the Holy Spirit) who came into Mary and was conceived of her. This is what scholars call "self-incarnation" and was the interpretation of Luke 1:35 given by the second century church fathers.

Hellenists (Jews who embraced Greek culture to an extent) was present in the second temple Judaism and in fact, well attested in the Acts of the Apostles. The gospel of John had a peculiar Hellenist perspective of the deity of Christ in that it taught of Christ as God using the concept of the Λογος (Logos). This Hellenic/Judaic belief in the divine Logos was not original to early Christianity but was independently present in the Jew, Philo of Alexandria (circa 50 CE) who also spoke of the logos as θεος. This means that the divine Logos was a prevalent view among the ancients even within the Jewish circles and the writer of the Johannine gospel found it useful for Christian evangelism to employ the concept into his Christ, to teach and edify the church of its early teaching found in Paul's epistles, that Jesus himself was God incarnate. In fact, Paul's high christology did not originate in him but is something he learned from earlier believers, so that the belief that Jesus was God incarnate predated Paul. Bible scholars have already come to a consensus that the belief in a divine Christ preceded Paul, so that the deity of Christ actually a pre-Paul, a very ancient Christian teaching indeed, having originated within the first year post-Easter (Richard Bauckham, Larry Hurtado, Bart Ehrman et al.).

Teaching Christ to be God incarnate using the Logos concept is by no means exclusive to John because Wisdom christology is present in the Synoptics and Wisdom is closely associated with the Logos concept, Wisdom being the Hebrew counterpart/equivalent of the hellenic Logos.

Conclusion

All the four gospels have Christ as God incarnate but only John taught Jesus to be such in a Hellenistic way by adopting the concept of the Logos. The Synoptics have shown Christ to be God incarnate in a Hebraic way through the identification of Christ with YHWH and Wisdom.

The way of John opened up the gospel to the gentiles. This was in line with Paul's who said that God spoke "first to the Jews and then to the Greeks" (the non Jews/gentiles). John presented Christ to the gentiles in a way that is faithful to the Hebrew faith. John translated Hebrew Wisdom into Greek Logos so that his message would be received by the gentiles. This shows that God speaks to us in a language that we can understand. In John, God speaks in a language that is inclusive, reaching not only the Jews but everyone else, So that every tongue - in heaven, on earth and under the earth - will acknowledge Jesus is Lord (= YHWH) (Phil. 2:11).

"I am not asking for a comparison between John’s gospel and the others"; nevertheless, a brief comparison is necessary:

• Tax collector Matthew's Gospel is very organized (e.g. written in 5 sections). Its intended audience is Jews (expectations of the biblical messiah), and Jesus is presented as a Ruler, to lead them.

• Servant by tradition Mark's Gospel is very concise (it's the shortest). Its intended audience is Romans (very practical and efficient), and Jesus is presented as a Servant, to get the job done.

• Physician Luke's Gospel is emotional (includes nativity and other non-doctrinal events). Its intended audience is Greeks (art and beauty), and Jesus is presented as Human, to be one of them.

• John's Gospel is precise (detailed and told in chronological order). Its intended audience is everyone, and Jesus is presented as God, to save them.

The first three Gospels were written to make it easier for Jews, Romans, and Greeks to understand and be converted to Christianity. They told the story in ways that were best suited for their specific audiences, stressing what would be important to them, and glossing over details that wouldn't.

If Matthew had lead with "Jesus is God", the Jews would have literally killed him, so he had to present Jesus as the promised Messiah. If Mark and Luke had lead with "Jesus is God", the Romans and Greeks would have thought: "Oh, not another one".

John's Gospel was written well after the others, for the benefit of all Christians. The Christian community was growing, and was ready to accept the concept of Jesus as God. By providing missing details and chronology, John complements what the other Gospels say and makes them easier to understand in context.

Even though written last, John's Gospel is the one that should be read and understood first; then the others can be better understood in his context.

The real question should have been: "Why did the other gospels write less clearly than John?".