“on the housetops.” The worship of the heavenly bodies was tied to the gods those heavenly bodies represented in the mind of the people (such as during the time of the Greeks the planet Mars representing the god Mars). The fact that these planets and stars were worshipped “on the housetops” shows that they were worshipped by families and friends, not only as some form of corporate worship done at a national level by idolatrous priests and pagan priests. Zephaniah’s words were not heeded, and so a half a generation or so later, in the time of Jeremiah, the practice was still going on (Jer. 19:13). In fact, although it seemed to have stopped after Jerusalem was destroyed, the women regretted stopping (Jer. 44:19). This worship of the heavenly bodies is parallel to the practice of astrology today, which is usually done on an individual level and involves the worship of the planets and stars. Although devotees of astrology would say they do not “worship” the stars, from a biblical perspective of looking to them for advice and guidance and giving one’s time to them, they are worshipping them and also disobeying Deuteronomy 4:9; 17:3; and 18:9-12.
“their ‘king’”. This is apparently a sarcastic referral to a god (perhaps Baal) that the people worshipped. Although the Hebrew text is debated and many versions prefer “Milcom” or “Moloch,” the meaning of the verse is not. The people of Israel were going through the motions of worshipping Yahweh but were also heavily involved in the worship of pagan gods. This kind of worship made a mockery of the first great commandment about not having any other gods.