The Greek verb antapodidōmi means to repay, to recompense, to give back in exact return. Composed of anti ('in return'), apo ('from'), and didōmi ('to give'), it carries the force of a corresponding return — giving back what is proportional to what was received, whether in blessing or judgment.
Romans 12:19 — 'It is mine to avenge; I will repay, says the Lord' — uses the cognate. Human vengeance is forbidden because God is the perfectly just recompenser. Antapodidōmi belongs to God alone.
Luke 14:14 promises that those who show hospitality to those who cannot repay will be 'repaid at the resurrection of the righteous.' Here God Himself becomes the recompenser of all acts of love done to the lowly — the theological logic underlying Jesus' teaching on heavenly reward.