Why did Satan fall to Earth?

In Biblical cosmology, "Heaven" is the sky, and "Earth" is the ground. Naturally, anything that falls from the sky is going to hit the ground.

The simple answer is that is was God’s permissive will to send the Devil to where He placed Adam and Eve in the garden.

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If Adam was on Mars then the Devil would have been sent there. So the answer is similar to ‘Why did God create the tree?’ ‘Why did God allow sin?’ ‘Why did God not turn the Devil into jelly-beans?’ ‘Why did God not prevent the temptation of Eve?’ All such questions have the same answer

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Sometimes when we have no clear reason why something happened, we can see the purpose in its effects. The initial effects of the Devil and his minions being cast upon the earth and expelled from the spiritual realm of God’s throne in heaven seems contrary to God’s will. The result is that man was tempted and fell under his power. The result was that sin had filled the world (not Mars) under his malice and control, so that now the world is completely flooded with mutual hatred, strife, envy, lust, anger, pride, fierceness, and rage, against one another; all which are the direct result of his being cast down and set free to temp Eve. The result is that man learned to hate God. Clearly this was not God’s true will only His permissive will. Yet God’s set the boundaries of many agents of free will to be used to work out His higher purposes of Grace.

What is the true result of this great and terrible thing? What is the result of sin multiplied by sin until each generation would be under Noah’s flood if God did not hold back His anger? The answer is that the more sin and hatred of God increased the more exceeding and praiseworthy is the glory of God shining brighter through it! HOW? In its total annihilation of sin and destruction and the redemption of the lost God haters, for which Jesus died!

20 The law was brought in so that the trespass might increase. But where sin increased, grace increased all the more, 21 so that, just as sin reigned in death, so also grace might reign through righteousness to bring eternal life through Jesus Christ our Lord. (Romans 5: 20-21)

In fact the reason for ‘everything’ even though it seems things went terribly wrong, is that it is according to God's pleasure and perfect will, intentional and permissive will. This does not excuse the sinfulness of sin or Gods will that none should sin, it only admits God knew every sin that man would ever commit and planned to provide atonement by the death of His Son, before the world was created. God does not live in time, so whatever happens tomorrow is no more distant than what happened before he fell. This includes choosing the location f where the Devil will live and how much power he is garneted.

Ephesians 1:3-6 is a typical verse declaring this truth, which has always been the position of great theologians:

3Praise be to the God and Father of our Lord Jesus Christ, who has blessed us in the heavenly realms with every spiritual blessing in Christ. 4For he chose us in him before the creation of the world to be holy and blameless in his sight. In love 5he c predestined us to be adopted as his sons through Jesus Christ, in accordance with his pleasure and will— 6to the praise of his glorious grace, which he has freely given us in the One he loves.

Notice everything was known 'before the creation' and that everything was done to the 'praise of his glorious grace'. Now I take these verses to mean that mankind's understanding and experience of God's grace, goodness and love, which can only lead us to praise and experience that grace, is at a 'higher realm' after the fall and salvation of mankind in Christ, then if there was no fall at all.

I found a quote by Martin Luther on the exact same question and he seems to have held the same view I propose:

If God should be asked at the last judgment, ‘Why did you permit Adam to fall?’ and he answered, ‘In order that my goodness toward the human race might be understood when I gave my Son for man’s salvation,’ we would say, ‘Let the whole human race fall again in order that thy glory may become known! Because thou hast accomplished so much through Adam’s fall we do not understand thy ways.’ “There is a threefold light: that of reason, that of grace, and that of glory.” (Luther's Works Volume 54, P385)

Martin Luther, Calvin, John Owen, Jonathan Edwards, etc. all held this view. Talking about God not wanting ‘robots’, is rather silly by comparison. It's a man center view and fairly earthly.

Subject likes this must be resolved into God's own good pleasure and grace, we can only have faith like the Apostle:

33 Oh, the depth of the riches of the wisdom and knowledge of God! How unsearchable his judgments, and his paths beyond tracing out! 34 “Who has known the mind of the Lord? Or who has been his counselor?” 35 “Who has ever given to God, that God should repay them?” 36 For from him and through him and for him are all things. To him be the glory forever! Amen. (Romans 11:33-36)