When the Garden was ON EARTH, before Adam and Eve knew how to distinguish between good and evil, God evidently allowed Satan to appear in the garden in a form that was unclean and clearly out of place there. Adam and Eve should have recognized that the serpent (Satan) did not belong there in that protected place. But they did not sense the danger, because their senses had not yet been trained to discern between good and evil. They were innocent and naive. They listened to the deception of the serpent and were caught in Satan’s trap.
That was all a part of their probationary test. Satan was allowed in the Paradise ON EARTH to tempt and deceive, as a part of the test of their obedience.
But in the Paradise Restored IN HEAVEN, there are no more temptations and probationary tests, because “nothing unclean” is allowed to go there. And Jesus has redeemed us from the curse and all that is related to it. That is how we know there will be no sin there. The tempter and deceiver (Satan) is not allowed to come into the Paradise in heaven. He has been permanently cast down into the Lake of Fire, in the opposite direction away from heaven in the UNSEEN realm above.
Even if Satan still has some limited influence in the SEEN realm on earth, he absolutely has NO influence in the UNSEEN realm in heaven. To say otherwise, is to destroy our hope for a sinless, safe, and secure afterlife. Here in Rev 21:22, the angel tells John that “nothing unclean (abomination, lying) shall ever come into it, but only those whose names are written in the Lamb’s book of life.” That is a precious and magnificent promise that we can count on experiencing in our afterlife in heaven. It is not a reality for us here in this life on earth.
See also related “Topic Studies & Terms”:
Related full “Study Series” (available upon request if not hyperlinked):
[For a more in-depth study see eschatology “Study Series 16 Lesson 9 Rev. Chapter 21”]