Psalms 18:25

With the merciful thou wilt shew thyself merciful; with an upright man thou wilt shew thyself upright;

God deals with people in keeping with their own character, showing himself merciful to the merciful and upright to the upright, and rewarding them according to their uprightness. The setting is the testimony of one who has kept the ways and statutes of God, who has remained upright before him, and who is assured of reward according to righteousness and the cleanness of hands and heart. The following verse carries the same principle still further, that God meets each person according to that person's character.

The spirit in which service is rendered matters, for humble trust and thankfulness are met with liberality on God's part, while bargaining for a fixed reward reveals failure to trust him. For this reason the verse calls for mercy and compassion toward those whose understanding is clouded. It requires showing mercy to the afflicted and meeting others where they are, and to refuse this places one outside the reach of God's love and mercy, while Isaiah 58 gives practical instruction for this merciful work.