Charles H. Spurgeon on Psalms 18:25

The dealings of the Lord in his own case, cause the grateful singer to remember the usual rule of God's moral government; he is just in his dealings with the sons of men, and metes out to each man according to his measure. "With the merciful thou wilt shew thyself merciful; with an upright man thou wilt shew thyself upright." Every man shall have his meat weighed in his own scales, his corn meted in his own bushel, and his land measured with his own rod. No rule can be more fair, to ungodly men more terrible, or to the generous man more honourable. How would men throw away their light weights, and break their short yards, if they could but believe that they themselves are sure to be in the end the losers by their knavish tricks! Note that even the merciful need mercy; no amount of generosity to the poor, or forgiveness to enemies, can set us beyond the need of mercy. Lord, have mercy upon me, a sinner.