Charles Ellicott Commentary 2 Kings 16:3

"But he walked in the way of the kings of Israel, yea, and made his son to pass through the fire, according to the abominations of the nations, whom Jehovah cast out from before the children of Israel." — 2 Kings 16:3 (ASV)

But he walked in the way. —See Notes on 2 Chronicles 28:2.

Made his son to pass through the fire. —The chronicler rightly explains this as a sacrifice by fire. That such an appalling rite is really intended may be seen by reference to 2 Kings 17:31; Jeremiah 19:5; Ezekiel 16:20; Ezekiel 23:37; and Jeremiah 32:35. The expression, “To make-to pass through the fire to Moloch” (Leviticus 18:21), may have originated, as Movers suggests, in the idea that the burning was a kind of passage to union with the deity, after the dross of the flesh had been purged away; or it may be a mere euphemism.

Ahaz appears to have been the first Israelite king who offered such a sacrifice. He, no doubt, regarded it as a last desperate resource against the oppression of his northern enemies. It is absurd to suppose that the king intended it in love to his child, as Thenius suggests . Such dreadful sacrifices were only made in cases of dire extremity (Compare to 2 Kings 3:27).

The heathen. —More particularly the Ammonites, who made such sacrifices to Molech or Milcom.