The only hopeful line in this prayer is the first, which reads, "O LORD, the God who saves me.” This is not to be dismissed lightly, for no person who knows that God is his Savior can ever utterly despair. However, the line is used as a mere address, a designation, and the psalm immediately passes to the fact that the writer has been crying to God "day and night," that is, unrelentingly and (as becomes apparent very quickly) without an answer. The writer has also been calling to God for a very long time—he has been afflicted from his youth (v. 15)—but God has not removed the cause of his suffering.

The powerful, descriptive phrase "dark night of the soul" is not much used today, but it was in the Middle Ages where it is found in the writings of the European mystics. It is a translation of the title of a book by the Spanish monk St. John of the Cross, known in English as The Ascent of Mount Carmel (1578-1580). What is the dark night of the soul? It is a state of intense spiritual anguish in which the struggling, despairing believer feels he is abandoned by God. This is what Psalm 88 describes. 

That grace has not failed yet, and it will never fail, because it comes from the inexhaustible supply of the infinite and eternally merciful and gracious God. We are eternally blessed if we know, worship and serve him.

Two things are said of those who will be brought to the worship of God in the days the psalmist envisions.

1. The people will acknowledge God. The word "acknowledge” in verse 4 is a translation of the Hebrew verb yadah, which has a rich variety of meanings. It can mean "know,” “acknowledge,” “understand," “be sure," "know about," "experience” and other variations. In the New International Version it is translated no less than 190 different ways to get as close as possible to the meaning. Here it means more than merely admitting that there is such a God as Jehovah or even acknowledging him as the one true God. It means coming to him in a saving relationship, bowing before him, and seeking to know him better. It means exactly what Jesus meant when he said in the great prayer recorded in John 17, "This is eternal life: that they may know you, the only true God, and Jesus Christ, whom you have sent" (v. 3).

The theme of these verses is Gentiles and Jews in Jesus' fold. Even more, it is the chief idea of the psalm. The idea is that in the latter days envisioned by the psalmist the Gentile nations will join the sons and daughters of Israel in acknowledging and worshipping the true God. I also call it the chief idea because it is from this that the psalmist gets his vision of a true brotherhood of nations and world peace.