Albert Barnes Commentary 1 Kings 19:2

"Then Jezebel send a messenger unto Elijah, saying, So let the gods do to me, and more also, if I make not thy life as the life of one of them by to-morrow about this time." — 1 Kings 19:2 (ASV)

The prophet had not long to wait before learning the intentions of the queen. A priest’s daughter herself, she would avenge the slaughtered priests; a king’s wife and a king’s child, she would not quail before a subject. That very night, a messenger declared her determination to bring about the prophet’s death within a day.

So let the gods ... - A common oath at that time (marginal references). The Greek Version prefixes another clause to this, which makes the oath even more forceful: As surely as you are Elijah and I am Jezebel, so let the gods...