Jamieson, Fausset and Brown on Zephaniah 1:5

5. worship the host of heaven--Saba: whence, in contrast to Sabeanism, Jehovah is called Lord of Sabaoth.

upon the housetops--which were flat (2Ki 23:5, 6, 12; Jr 19:13; 32:29).

swear by the Lord--rather, "swear to Jehovah" (2Ch 15:14); solemnly dedicating themselves to Him (compare Is 48:1; Ho 4:15).

and--"and yet (with strange inconsistency, 1Ki 18:21; Eze 20:39; Mt 6:24) swear by Malcham," that is, "their king" [Maurer]: the same as Molech (see on Am 5:25), and "Milcom the god of ... Ammon" (1Ki 11:33). If Satan have half the heart, he will have all; if the Lord have but half offered to Him, He will have none.