We then are close in our thinking...though I'm not sure. When you say does God demand perfection or sinlessness do you mean in order to get to heaven?
This is actually quite simple, and not at all a new belief. God established a covenant with Adam and Eve based on their perfect adherence to the Law. For them, and their progeny, to inherit everlasting life and enjoy continued harmony with God, the representatives, i.e., Adam and Eve, must keep the law perfectly. They failed, and in doing so plunged themselves and their progeny into ruin. Man fell from grace, he inherited a sinful nature, every part of his being was corrupted by the stain of sin, yada, yada, yada.
Now God, being merciful, didn't leave man in that state of destitution. He established a new covenant. I'll call it the covenant of grace. In this covenant, God mercifully established a plan by which His elect would be spared from His wrath. God
still required perfect obedience in this new covenant. However, unlike the covenant He made with Adam, this new covenant, which was established amongst the Godhead, recognized man's inherent inability to meet the requirement of perfection. Therefore, as part of the covenant, God the Father sent God the Son to be a propitiation. Christ was sent to fulfill the requirement of perfect obedience that the first Adam failed to meet. Jesus fulfilled the requirement of perfection and God graciously deigns to credit the believer with the righteousness of Christ.
So you see, perfection is, and always has been, required. The difference is that it is the perfection of Christ for which we are credited and, therefore, we stand before God as justified (this means to be pronounced just, or without sin).
We are tarnished with the sinful nature until heaven where the curse is removed according to Revelation...therefore sinlessness cannot be achieved on this side of heaven. Aiming for perfection can be achieved.
Well, I would disagree to the extent that those that are born again are given a new nature but, for the record, I also acknowledge that the weakness of our flesh will prevent sinlessness this side of Heaven.