1 Kings 18:40 - Ellicott's Commentary On The Whole Bible

Slew them. — This ruthless slaughter of Baal’s prophets, as a judgment on their idolatry and perversion of the people, belongs alike to the fierce righteousness of the character of Elijah, and to the spirit of the old Law. (See, for example, Deuteronomy 13:6-18; Deuteronomy 17:2-7.) The law was adapted (as in the terrible crucial example of the slaughter of the Canaanites) to the “hardness of men’s hearts.” In the imperfect moral and religious education of those times, it did not recognise the difference between moral and political offences punishable by human law, and the religious sin or apostasy which we have been taught to leave to the judgment of God alone; and it enjoined an unrelenting severity in the execution of righteous vengeance, which would be morally impossible to us, who have been taught to hate the sin, and yet spare, as far as possible, the sinner. The frequent quotation of such examples by Christians — of which Luke 9:54 is the first example — is a spiritual anachronism. In this particular case, however, it is also to be remembered that those slain were no doubt implicated in the persecution headed by Jezebel, and that the Baal-worship was a licentious and perhaps bloody system. Elijah, presiding over the slaughter which dyed the waters of the Kishon with blood, felt himself the avenger of the slaughtered prophets, as well as the instrument of the judgment of God.