This psalm appears to describe the destruction of Jerusalem and the temple by the Chaldeans. The deplorable case of the people of God, at the time, is spread before the Lord, and left with him. They plead the great things God had done for them.
If the deliverance of Israel out of Egypt was encouragement to hope that he would not cast them off, much more reason have we to believe, that God will not cast off any whom Christ has redeemed with his own blood.
Infidels and persecutors may silence faithful ministers, and shut up places of worship, and say they will destroy the people of God and their religion together. For a long time they may prosper in these attempts, and God's oppressed servants may see no prospect of deliverance; but there is a remnant of believers, the seed of a future harvest, and the despised church has survived those who once triumphed over her.
When the power of enemies is most threatening, it is comfortable to flee to the power of God by earnest prayer.