Psalms 56:12

“I will render praises--will pay what I have vowed.”

“Thy vows are upon me, O God - The word “vow” means something promised; some obligation under which we have voluntarily brought ourselves. It differs from duty, or obligation in general, since that is the result of the divine command, while this is an obligation arising from the fact that we have “voluntarily” taken it upon ourselves. The extent of this obligation, therefore, is measured by the nature of the promise or vow which we have made; and God will hold us responsible for carrying out our vows. Such voluntary obligations or vows were allowable, as an expression of thanksgiving, or as a means of exciting to a more strict religious service, under the Mosaic dispensation Genesis 28:20;…”

“Thy vows - I had made vows to express my gratitude, and resolve to perform them. Psalms 56:13”

“Thy: Psa 66:13, Psa 66:14, Psa 76:11, Psa 116:14-19, Psa 119:106; Gen 28:20-22, Gen 35:1-3; Num 30:2-16; Sa1 1:11, Sa1 1:24-28; Ecc 5:4-6 I will: Psa 9:1-3, Psa 21:13, Psa 59:16, Psa 59:17; Isa 12:1 Psalms 56:13”

“In prospect of his deliverance the poet promises beforehand to fulfil the duty of thankfulness. עלי, incumbent upon me, as in Pro 7:14; Sa2 18:11. נדריך, with an objective subject, are the vows made to God; and תּודות are distinguished from them, as e.g., in Ch2 29:31. He will suffer neither the pledged שׁלמי נדר nor the שׁלמי תּודה to be wanting; for - so will he be then able to sing and to declare - Thou hast rescued, etc. The perfect after כּי denotes that which is then past, as in Psa 59:17, cf. the dependent passage Psa 116:8. There the expression is ארצות החיּים instead of אור החיּים (here and in Elihu's speech, Job 33:30). Light of life ( Joh 8:12) or of the living (lxx τῶν ζώντων)…”