Matthew Henry Commentary Psalms 64:7-10

"But God will shoot at them; With an arrow suddenly shall they be wounded. So they shall be made to stumble, their own tongue being against them: All that see them shall wag the head. And all men shall fear; And they shall declare the work of God, And shall wisely consider of his doing. The righteous shall be glad in Jehovah, and shall take refuge in him; And all the upright in heart shall glory." — Psalms 64:7-10 (ASV)

When God brings upon people the harm they have desired for others, it is a weight sufficient to sink a person to the lowest hell. Those who love cursing, it will come upon them.

Those who witness this will understand and observe God's hand in everything; unless we do so, we are not likely to profit from the dispensations of Providence.

The righteous will be glad in the Lord; not glad of the misery and ruin of their fellow creatures, but glad that God is glorified, his word fulfilled, and the cause of injured innocence effectively pleaded. They rejoice not in people, nor in themselves, nor in any creature, or creature enjoyments, nor in their wisdom, strength, riches, or righteousness; but in Christ, in whom all the seed of Israel are justified and glory, and in what he is to them and has done for them.