"Say to the people of Israel, Any one of the people of Israel or of the strangers who sojourn in Israel who gives any of his children to Molech shall surely be put to death. The people of the land shall stone him with stones.
One of the horrific pagan rituals of the time was that of child sacrifice. The nations surrounding Israel would murder their children in unspeakable ways to appease their false gods. Molech was one such pagan god.
The Israelites were to keep themselves free from this practice and were to kill any visitors who did these things.
Stoning was a method for killing those who broke certain laws. It was not a fast way to die, allowing a sense of justice at the suffering of the guilty. However, it also involved the whole community throwing the stones, and this meant the people each had a hand in the death of the person. Because of this it was unlikely that someone would be falsely convicted because those accusing had to live with the death at their own hands.