Like all scripture, this is a very rich text. For context, at the beginning of the book of Jonah, the LORD spoke to prophet Jonah and told him to go and cry against Nineveh for their wickedness had come up before Him. The prophet runs from the presence of the LORD and boards a ship going south to Tarshish. The LORD sends a great wind upon the seas and Jonah is cast out of the ship at his own request after the mariners realize that this great tempest has befallen them because of Him. The LORD prepares a great fish that swallows Jonah and he stays in the belly of the fish for three days and three nights. It is from the belly of the fish that the prophet cries out to God in chapter 2.

At the end of his prayer he makes the profound statement in verses 8 through 10. The original hebrew translates verse 8 thus

• observe as šāmar meaning to guard, take heed, preserve, regard
• lying as šāv’ meaning desolating, idolatry, uselessness, false
• vanities as heḇel meaning emptiness or vanity, something transitory and unsatisfactory
• mercy as ḥeseḏ meaning kindness, favor, lovingkindness

Some Bible versions write, Those who regard worthless idols forsake their own mercy (NKJV). ‘Observing lying vanities’ is multifaceted. A lying vanity is something false that is passing away. It could be an idol, a work of the flesh and the flesh itself, an illness, etc. When man takes heed to it; acknowledging it and preserving a consciousness of it, they reject the grace of God that enables them to overcome evil, the flesh and all its works. The life of faith that we are called to live is one where we only acknowledge every good thing which is in us in Christ Jesus (Philemon 6).

BUT in verse 9 emphasizes that what the prophet says next differs from what he has said before. BUT I will sacrifice unto thee with the voice of thanksgiving; I will pay that that I have vowed. Salvation is of the LORD. This is the believer’s part; acknowledging that the LORD has saved us by His grace and offering praise and thanksgiving to Him.