Romans 1:14-15 — I am debtor both to the Greeks, and to the Barbarians; both to the wise, and to the unwise. So, as much as in me is, I am ready to preach the gospel to you that are at Rome also.
Debtor — Paul was obligated because
He had to "pay back" in service what Christ's love had done for him
It was his assignment.
Greeks (civilized nations, including Rome) and barbarians (all uncivilized nations) — those Paul had to pay his debt to
Wise and unwise — cultured and uncultured, people of all degrees
Ready to preach — Paul's preparation was complete. The word translated "ready" indicates readiness and inclination.
Preach the gospel — Paul was a herald giving a proclamation.