The point of Jesus and the sacrifice He did is that no one could ever keep the law perfectly. They were gonna kill the woman for being adulterous, but they were all adulterous too, as well as many other sinful things.
What then? are we better than they? No, in no wise: for we have before proved both Jews and Gentiles, that they are all under sin;
10 As it is written, There is none righteous, no, not one:
Therefore by the deeds of the law there shall no flesh be justified in his sight: for by the law is the knowledge of sin.
Anyone who doesn't accept Jesus's sacrifice for their sins will go to hell because:
10 For whosoever shall keep the whole law, and yet offend in one point, he is guilty of all.