17 “In me, O God, are Your vows, which I will render of praise to You”. “Vow ye, and render to the Lord your God.” What vow, what render? Perchance those animals which were offered at the altars aforetime? No such thing offer thou: in yourself is what you may vow and render. From the heart's coffer bring forth the incense of praise; from the store of a good conscience bring forth the sacrifice of faith. Whatsoever thing you bring forth, kindle with love. In yourself be the vows, which you may render of praise to God.
Of what praise? For what has He granted you? “For You have rescued my soul from death”. This is that very life which he tells out to Him: “O God, my life I have told out to You.” For I was what? Dead. Through myself I was dead: through You I am what? Alive. Therefore “in me, O God, are Your vows, which I will render of praise to You.” Behold I love my God: no one does tear Him from me: that which to Him I may give, no one does tear from me, because in the heart it is shut up.
With reason is said with that former confidence, “What should man do unto me?” Let man rage, let him be permitted to rage, be permitted to accomplish that which he attempts: what is he to take away? Gold, silver, cattle, men servants, maid servants, estates, houses, let him take away all things: does he by any means take away the vows, which are in me, which I may render of praise to God? The tempter was permitted to tempt a holy man, Job; in one moment he took away all things: whatever of possessions he had had, he carried off: took away inheritance, slew heirs; and this not little by little, but in a crowd, at one blow, at one swoop, so that all things were on a sudden announced: when all was taken away, alone there remained Job, but in him were vows of praise, which he might render to God, in him evidently there were: the coffer of his holy breast the thieving devil had not rifled, full he was of that wherefrom he might sacrifice.
Hear what he had, hear what he brought forth: “The Lord has given, the Lord has taken away; as has pleased the Lord, so has been done: be the name of the Lord blessed.” O riches interior, whither thief does not draw near! God Himself had given that whereof He was receiving; He had Himself enriched him with that whereof to Him he was offering that which He loved. Praise from you God requires, your confession God requires. But from your field will you give anything? He has Himself rained in order that you may have.
From your coffer will you give anything? He has Himself put in that which you are to give. What will you give, which from Him you have not received? “For what have you which you have not received?” From the heart will you give? He too has given faith, hope, and charity: this you must bring forth: this you must sacrifice. But evidently all the other things the enemy is able to take away against your will; this to take away he is not able, unless thou be willing. These things a man will lose even against his will: and wishing to have gold, will lose gold; and wishing to have house, will lose house: faith no one will lose, except him that shall have despised her.
Source: The Enarrations, or Expositions, on the Psalms (New Advent)