C. F. Keil and Franz Delitzsch on 1 Kings 18:20

1Ki 18:20 Elijah’s contest with the prophets of Baal. - Ahab sent through all Israel and gathered the prophets (of Baal) together upon Mount Carmel. According to 1Ki 18:21, 1Ki 18:22, and 1Ki 18:39, a number of the people (“all the people”) had also come with them. On the other hand, not only is there no further reference in what follows to the 400 prophets of Asherah (cf. 1Ki 18:25 and 1Ki 18:40), but in 1Ki 18:22 it is very obvious that the presence of the 450 prophets of Baal alone is supposed. We must therefore assume that the Asherah prophets, foreboding nothing good, had found a way of evading the command of Ahab and securing the protection of Jezebel.It is true that in 1Ki 18:22 the lxx have this clause, καὶ οἱ προφῆται τοῦ ἄλσους (i.e., האשׁרה) τετρακόσιοι, which Thenius regards as an original portion of the text, though without observing the character of the lxx. If the Asherah prophets had also been present, Elijah would not only have commanded the prophets of Baal to be seized and slain (1Ki 18:40), but the Asherah prophets also. From the principle a potiori fit, etc., it may be possible to explain the omission of the Asherah prophets in 1Ki 18:25, but not in 1Ki 18:40.

King Ahab also appeared upon Carmel (cf. 1Ki 18:41), as he had no idea of Elijah’s intention, which was by no means “to prove to the king that he (Ahab) and not Elijah had brought Israel into trouble” (Vat., Seb. Schm.), but to put before the eyes of the whole nation a convincing practical proof of the sole deity of Jehovah and of the nothingness of the Baals, that were regarded as gods, and by slaying the priests of Baal to give a death-blow to idolatry in Israel.