The Bible says in the book Revelation that God will imprison Satan for one thousand years and will then throw Satan into the Lake of Fire forever. Since God has the power to restrain Satan why didn’t He do so as soon as Satan rebelled? Why didn’t God keep Satan out of the Garden of Eden and away from Adam and Eve? Why did God allow Satan to tempt men to sin?
The Bible does not give a direct answer to this question. Despite that, what the Bible reveals about the character and purposes of God helps in the formulation of an answer. Romans 9:21-23 speaks of the Sovereignty of God in His dealings with men. God allowed some, like Pharaoh, to persist in sin to show all mankind His wrath, power, patience and glory. God in His grace and wisdom allowed Satan to tempt Adam and Eve so that through their sin His wrath, patience, mercy and glory would be known to all people. Because man sinned we learned first hand that God is Holy and always punishes sin. We also learned that God is an overwhelmingly gracious God who gave His Son to die for our sin. Through sin we learn about God what we could never have known any other way. The sin of Satan and the fall of man allowed God to show that His grace is far greater than our sin.
The righteous angels study the gospel looking from the outside into something mysterious to them. (1 Peter 1:12) The angels do not understand the mercy and grace of God in the same way men do because the angels are not recipients of His grace. In the end, the plan of God that allowed sin will result in incredible, eternal praise to Him. “Thou art worthy to take the book, and to open the seals thereof: for thou wast slain, and hast redeemed us to God by thy blood out of every kindred, and tongue, and people, and nation; And hast made us unto our God kings and priests: and we shall reign on the earth.” (Revelation 5:9-10) All the redeemed will praise God for His righteous judgment of the wicked. (Revelation 19:1-2) The plan of God which allowed sin also allows people the opportunity to truly and personally know “the grace of God that brings salvation.” (Titus 2:11)
The words at the end of Genesis apply to this question. “You thought evil against me, but God meant it unto good.” (Genesis 50:20) Satan was bent on the destruction of man, and God allowed Satan to work great evil. All the evil Satan desired also accomplishes the eternal good that God ordained. God allowed Satan to tempt man for our eternal good and His eternal praise. Though a full answer cannot be given to this question we can rest in the character of God. God is perfect, wise and good. The Judge of the whole earth will do right. (Genesis 18:25) You can trust Him.