But I will sacrifice unto thee with the voice of thanksgiving; I will pay that that I have vowed. Salvation is of the LORD.

Wesley's Notes

2:9 Vowed - Which probably was to go to Nineveh, and preach what God commanded him. The Lord - He only can save.

Jamieson-Fausset-Brown Bible Commentary

9. I will sacrifice . thanksgiving-In the believing anticipation of sure deliverance, he offers thanksgivings already. So Jehoshaphat (2Ch 20:21) appointed singers to praise the Lord in front of the army before the battle with Moab and Ammon, as if the victory was already gained. God honors such confidence in Him. There is also herein a mark of sanctified affliction, that he vows amendment and thankful obedience (Ps 119:67).

Matthew Henry's Concise Commentary

2:1-9 Observe when Jonah prayed. When he was in trouble, under the tokens of God's displeasure against him for sin: when we are in affliction we must pray. Being kept alive by miracle, he prayed. A sense of God's good-will to us, notwithstanding our offences, opens the lips in prayer, which were closed with the dread of wrath. Also, where he prayed; in the belly of the fish. No place is amiss for prayer. Men may shut us from communion with one another, but not from communion with God. To whom he prayed; to the Lord his God. This encourages even backsliders to return. What his prayer was. This seems to relate his experience and reflections, then and afterwards, rather than to be the form or substance of his prayer. Jonah reflects on the earnestness of his prayer, and God's readiness to hear and answer. If we would get good by our troubles, we must notice the hand of God in them. He had wickedly fled from the presence of the Lord, who might justly take his Holy Spirit from him, never to visit him more. Those only are miserable, whom God will no longer own and favour. But though he was perplexed, yet not in despair. Jonah reflects on the favour of God to him, when he sought to God, and trusted in him in his distress. He warns others, and tells them to keep close to God. Those who forsake their own duty, forsake their own mercy; those who run away from the work of their place and day, run away from the comfort of it. As far as a believer copies those who observe lying vanities, he forsakes his own mercy, and lives below his privileges. But Jonah's experience encourages others, in all ages, to trust in God, as the God of salvation.