Adam Clarke on Psalms 18:25

With the merciful thou wilt show thyself merciful - Thou wilt deal with men as they deal with each other. This is the general tenor of God's providential conduct towards mankind; well expressed by Mr. Pope in his universal prayer: - "Teach me to feel another's wo;To hide the fault I see:

The mercy I to others show,That mercy show to me."

It is in reference to this that our Lord teaches us to pray: "Forgive us our trespasses, as we forgive them that trespass against us." If we act feelingly and mercifully towards our fellow creatures, God will act tenderly and compassionately towards us. The merciful, the upright, and the pure, will ever have the God of mercy, uprightness, and purity, to defend and support them.