If “The Fall” was caused by just one sin from the very first humans and all humans since have sinned, what are our chances of remaining sinless in heaven? I assume we would still have our gift of free will, so surely someone would sin?
There is no chance whatsoever that we will, once we are in heaven, fall again into sin, for at least two important reasons. First, God has so promised. The picture we are given of the eternal blessing we receive in Christ includes our being utterly pure, white, without spot or blemish. That we will stay in this state will at least come to pass on the basis of God’s promise. Remember when God stood with Joshua looking out at the city of Jericho and its rather substantial wall. God said, “See, I have delivered the city into your hands.” God’s Word is so certain that what He has spoken, though it has not yet come to pass, that it can be spoken of as in the past tense. I call this tense, “God’s prophetic past.”
Secondly, and perhaps ironically, it is precisely our free will which will be the means by which God’s promise is brought to pass. All moral beings, men, angels and even God Himself are free to choose. All of them, however, in their freedom, always choose according to their nature. God, for instance, could sin, if He so desired. But He does not so desire, for He is altogether good. He is “free” to do evil in one sense, but not free in another sense. No one forces Him to do good, but He will always and only do good.
When we enter into our reward, we will be fully and finally sanctified. That is, we will be fully and finally holy. There will be no more sin, no more desire for sin in us. We will have no more sin nature in us; we will be altogether good. We, like God Himself, will be free to do evil, were we so to desire, but we would never so desire because we will be altogether good. This is one of the greatest promises of eternity, that the struggle within ourselves between the old and the new man, between the Spirit and the flesh will be over. We will be at peace; we will enter into rest. Our warfare will have ended.
It is good and right for us to mourn the fall, to look deeply into all the destruction wrought by our parents’ first sin. But we must in turn look forward to the fullness of the promises of God. We will walk with Him in the garden again, unashamed and at peace. This is what Jesus has brought to pass for us, His beloved bride. We will be what we were made to be, and will stay so forevermore.