Who remembers the following phrase?

Woman taken in Adultery (1524-27) – Ortolano
‘Let anyone among you who is without sin cast the first stone’.
The painting at the right shows the exact moment when Jesus wrote in the ground those words. It is imperative to know what the Bible says about this event
John 7:53–8:11
Then each of them went home, while Jesus went to the Mount of Olives. Early in the morning he came again to the temple. All the people came to him and he sat down and began to teach them. The scribes and the Pharisees brought a woman who had been caught in adultery; and making her stand before all of them, they said to him, ‘Teacher, this woman was caught in the very act of committing adultery. Now in the law Moses commanded us to stone such women. Now what do you say?’ They said this to test him, so that they might have some charge to bring against him. Jesus bent down and wrote with his finger on the ground. When they kept on questioning him, he straightened up and said to them, ‘Let anyone among you who is without sin be the first to throw a stone at her.’ And once again he bent down and wrote on the ground. When they heard it, they went away, one by one, beginning with the elders; and Jesus was left alone with the woman standing before him. Jesus straightened up and said to her, ‘Woman, where are they? Has no one condemned you?’ She said, ‘No one, sir.’ And Jesus said, ‘Neither do I condemn you. Go your way, and from now on do not sin again.’
It is no doubt that the event is framed to focus on the mercy of Jesus, but I want to be more subtle and focus on the event before Jesus wrote on the ground.

The Woman Taken in Adultery – Rembrandt (1644)
Moses’s Law mentioned in the paragraph above, tell us that is a duty to kill a woman or men by committing adultery, written in the old testament. (Leviticus 20:10).
Now is interesting that religion understood this, improving their own moral for being better off as society. But, Why this event that has happened 2,000 years ago (more or less) is still happening today?. A question on the side, let hypothesise that nowadays Christianity is based on Moises Law, we as westerners, Would still be throwing stones to adultery woman or men? as some more orthodox Islamic cultures still do?.
A deeper question is, Why Christianity argues that morality is coming from God as a unique and stable truth, when there is a a radical change on moral based initially on Moses’s Law and after on Jesus’s Law?