Not all debts are related to money. When Romans 13:8 is read in conjunction with the previous verse (Rom.13:7), we see that giving honour, respect and obedience are also debts that we owe to others.
Parents : Children must obey their parents as long as they live at home. But they must honour them as long as their parents are alive (Eph.6:1-3). Honouring our parents is not a favour that we do to them but a lifelong debt that we owe them.
Husbands and wives : Wives are commanded to respect their husbands and to be subject to them (Eph.5:22,33). This is a debt that every wife owes to her husband. And husbands are commanded to love their wives (Eph.5:25,33). This too is a lifelong debt that every husband owes to his wife.
All men : We are commanded to honour ALL human beings (1 Pet.2:17). This is a debt that we owe to ALL human beings - poor and rich. Any believer who speaks disrespectfully to another human being is disobeying this command and is in debt. He must clear such a debt by apologizing - both to God and to the person concerned.
Gratitude for Spiritual Ministry
Finally: We owe an immense debt of gratitude to those who have ministered to us spiritually. We are commanded in a number of places in the New Testament to appreciate, express our gratitude and honour those who serve us in the Name of the Lord and whose ministry has blessed us.
"Honour those leaders who work so hard for you, who have been given the responsibility of guiding you. Overwhelm them with appreciation and love!" (1 Thess.5:12,13- Message).
This is a debt that is very easy to pay. Yet most believers never pay it. They honour and appreciate doctors who have treated them and cured them far more than they honour and appreciate spiritual ministries that have blessed them. That only proves that they value their physical health more than they value their spiritual health.
Let us seek with all our hearts to live free from every form of debt at all times.
Owe nothing to anyone.