Many different themes are treated in the Book of Psalms. For example, one psalm praises Yahweh for coming to the defense of his people when the Assyrian armies invaded Judah. The sudden withdrawal of the army, leaving the city of Jerusalem standing, was indeed an occasion for great rejoicing. Yahweh's love for the poor and the oppressed is the theme of Psalm 146. Sorrow and discouragement because of the fate that befell the nation when the people were taken into captivity by a foreign power are expressed in the prayers that are recorded in Psalms 42 and 43. The same attitude can be found in Psalm 22, in which the author cries out from the depths of his soul, "My God, my God, why have you forsaken me?" The Babylonian captivity is the setting for Psalm 137, which reports, "By the rivers of Babylon we sat and wept when we remembered Zion." Psalm 119, the longest one in the entire book, is an alphabetical poem written in praise of the Law.
The psalms' teachings are difficult to summarize because their main purpose is not instruction but expressions of the heart made in the spirit of worship. Nevertheless, certain ideas are set forth in the psalms that are essential to the purposes for which they were written, including the reality and significance of Yahweh in relation to the experiences of individuals and the nation as a whole. True, the conception of Yahweh is not always the same in the different psalms, but this difference is due to the fact that each author must find for himself the conception that seems most adequate to him. Sometimes Yahweh is portrayed as a god of loving kindness and mercy, but at other times he is a god of wrath who brings destruction on those who disobey his commands. Always Yahweh is presented as an everlasting God, one who is omnipotent and omniscient, and whose power and goodness endure throughout all generations.
