It seems fair to say that some moral commitments find their impulse in the desire to render back to God some good because of the help he has given in distress.
How are we to understand this connection and its relationship to faith in future grace? And why is rendering back to God the payment of our vows not an example of the debtor’s ethic?
What keeps the paying of vows from the dangers of the debtor’s ethic is that the “payment” is, in reality, not an ordinary payment, but another act of receiving which magnifies the ongoing grace of God. It does not magnify our resourcefulness. We can see this in . . . Psalm 116:12-14.
The psalmist’s answer to his own question, “What shall I render to the Lord for all his benefits?” is, in essence, that he will go on receiving from the Lord so that the Lord’s inexhaustible goodness will be magnified.
First, lifting up the cup of salvation signifies taking the Lord’s satisfying salvation in hand and drinking it and expecting more. This is why I say that “paying” back to God in these contexts is not an ordinary payment. It is an act of receiving.
Second, this is also the meaning of the next phrase: “I shall call upon the name of the Lord.” What shall I render to God for graciously answering my call? Answer: I shall call again. I will render to God the praise and the tribute that he is never in need of me, but is always overflowing with benefits when I need him (which I always do).
Then the psalmist says, in the third place, “I will pay my vows to the Lord.” But how will they be paid? They will be paid by holding up the cup of salvation and by calling on the Lord. That is, they will be paid by faith in future grace.
Future Grace, Multnomah Books (Colorado Springs, CO), pages 37-38