I am a debtor both to Greeks and to barbarians, both to wise and to unwise.

Romans 1:14
I am a debtor both to Greeks and to barbarians, both to wise and to unwise.

This is how Paul views himself. He was totally set free by the bondage of the Law. With his new found freedom, he knew that Yshua paid the price for him which he can never repay. On his own free will, he chose to be a bondservant to Yshua and devoted his life to tell others about the Kingdom of God, so that they too can be set free. Clearly not every believer do what Paul did, and there is no condemnation on others. Paul has set an example which is pleasing to God - it is something for us to be reminded of from time to time even if we don't exactly follow in his footsteps.