The Psalms may be read, of course, but they were first designed to be sung. They are inspired song. The Spirit inspired the authors who wrote the various Psalms, and from when they were first written in Old Testament times, they were also sung. The Spirit’s fruit of “joy” is clearly evidenced in the Psalms of a joyous character—”Alleluia! (‘Praise Yahwheh’). The Spirit’s fruit of “peace” is seen in the Psalms of lament, confession, or even the imprecatory Psalms! These also produce joy in a sense. Finally, the Spirit’s fruit of “patience” and “faithfulness,” and even the related idea endurance, is produced by the more didactic, teaching Psalms, “For whatever was written in former days was written for our instruction, that through endurance and through the encouragement of the Scriptures we might have hope.” (Rom 15:4)
The evidence of their being sung is all over the psalms. There are Psalms that were set to specific music, like “To the lilies” for Psalm 69. There are Psalms that were supposed to be supported by specific instruments, like Psalm 61. There are also 55 Psalms addressed “to the choirmaster” (e.g., Psalm 4). Finally, the Psalms themselves are full of the call to “sing praises.” “Sing praises to God, sing praises! Sing praises to our King, sing praises! For God is the King of all the earth; sing praises with a psalm!” (Ps 47:6). Or the more familiar traditional Psalm for Matins: “Let us come before his presence with thanksgiving, and make a joyful noise unto him with psalms.” (Ps 95:2)
The music is meant to carry the words not only into our minds, but when paired with music the Psalm enters our heart and naturally comes out of our mouth. The music also assists in preaching the Word properly to us. Simply put, for example, a happy tune with a happy psalm, a minor one with a somber one. Besides this, the music can help teach the theology of the Psalm or even put the Psalm back into its proper context. Context is important for all Scripture passages, and pulling them out of context can lead to misunderstanding. This danger exists for all passages of Scripture, but this danger is especially so for the Old Testament wisdom books (Job, Psalms, Proverbs, Ecclesiastes, Song of Solomon) in general but the Psalms in particular.
The Wisdom books, especially the Psalms, are Hebrew poetry. Hebrew poetry does not rhyme like English poetry. Instead, Hebrew poetry works by way of parallelism, i.e., two phrases are placed next to each other to further expand the meaning. This parallels can happen in many ways, mostly by comparing or even contrasting ideas. Let us use Psalms 23:1 is an example. “The LORD is my Shepherd; I shall not want.” Why “shall I not want”? Because “the Lord is my Shepherd.” What is the benefit of “YAHWEH being my Shepherd”? It means “I shall not want.”
The following Psalm tones and settings are designed for various reasons. They might be meant for specific Psalms, for a specific genre of Psalms, or for no particular Psalm. The settings are to offer another expression of the Psalm in song. They could also be designed to help put the Psalm as whole, along with each of its verses, back into context so we better understand what the Spirit is saying through the Psalm author.