They that observe lying vanities forsake their own mercy. They that worship idols, who are nothing, mere vanity and lies, and deceive those that serve them, these forsake the God of their lives, and of their mercies; and so do all such who serve divers lusts and pleasures, and pursue the vanities of this life; and also those who follow the dictates of carnal sense and reason, to the neglect of the will of God, and obedience to his commands; which was Jonah's case, and is, I think, chiefly intended.
The Targum, Syriac version, and so Jarchi, and most interpreters, understand it of worshippers of idols in general; and Kimchi of the mariners of the ship Jonah had been in; who promised to relinquish their idols, but did not; and vowed to serve the Lord, and sacrifice to him, but did not perform what they promised.