““For who has known the mind of the Lord, or who has been his counselor?” “Or who has given a gift to him that he might be repaid?”” (Romans 11:34–35, ESV)
I have heard well intentioned believers say that they were serving God in order to pay Him back for their salvation. I have heard others call this the debtor’s ethic. It is impossible to pay God back by doing good works.
Let me give you this example from a scene I saw on National Lampoon’s Christmas. In it Clark Griswold’s cousin Eddie was penniless and could not get Christmas gifts for his children. Clark offers to help Eddy by purchasing gifts for Eddie to give away. Then Eddie gives Clark a shopping list and tells Clark, “And if it wouldn’t be too much, I’d like to get something for you Clark. Something really nice.” In other words, he was telling Clark to buy his own gift for Eddie to give to him.
This is exactly the problem with the debtor’s ethic. First of all, the cost of our salvation was priceless. We had an infinite debt of sin. The price paid for this debt was the death of Jesus Christ on the cross. This was a price too high for us to pay, infinitely higher by the way. For that reason, we needed to be saved by grace through faith alone, apart from any works of righteousness. We could never purchase our own salvation.
Moreover, even after God saving us by grace, we still could never pay back all that He has done for us, because we need grace to do good works. Paul stated it like this, “But by the grace of God I am what I am: and his grace which was bestowed upon me was not in vain; but I laboured more abundantly than they all: yet not I, but the grace of God which was with me.” (1 Corinthians 15:10, KJV 1900) Paul labored hard, but it was not him but God’s grace at work in him.
In other words, we need God’s grace to do good works and thus every good work we do requires more grace so that we do not pay back anything. In fact, by the principle of a debtor’s ethic, what we really do is accumulate more debt.
So why do we serve God after we are saved? It is because of God’s grace at work in us. He has placed within us by His Spirit, spiritual gifts to use for his glory in building up the church, along with the power and the unction to do so. Moreover, He has created good works for us to do (Eph 2:10). We serve because we love him and are grateful for what He has done. However, we can never pay Him back. We must just rejoice in our salvation, serve as He leads, and give thanks for all He has done.