But he walked in the way of the kings of Israel; indeed he made his son pass through the fire, according to the abominations of the nations whom the Lord had cast out from before the children of Israel. (2 Kings 16:3)
This describes Ahaz’s participation in the worship of Molech. The pagan god (or, demon, more accurately) Molech was worshipped by heating a metal statue representing the god until it was red hot, then placing a living infant on the outstretched hands of the statue, while beating drums drowned out the screams of the child until it burned to death.
In Leviticus 20:1-5, God pronounced the death sentence against all who worshipped Molech, saying: I will set My face against that man, and will cut him off from his people, because he has given some of his descendants to Molech, to defile My sanctuary and profane My holy name (Leviticus 20:3).
Sadly, even a man as great as Solomon at least sanctioned the worship of Molech and built a temple to this idol (1 Kings 11:7). One of the great crimes of the northern tribes of Israel was their worship of Molech, leading to the Assyrian captivity (2 Kings 17:17). King Manasseh of Judah gave his son to Molech (2 Kings 21:6). Up to the days of King Josiah of Judah, Molech worship continued, because he destroyed a place of worship to that idol (2 Kings 23:10).
So Ahaz rested with his fathers, and was buried with his fathers in the City of David. Then Hezekiah his son reigned in his place. (2 Kings 16:20)
Ahaz was an evil King but he had a very godly son – Hezekiah. This is a mystery to me. Some very godly parents have evil children.