Psalm 42‘s position in the Psalter provides a good example of how ancient editors group these holy poems. Psalms 42-45 seem to be grouped because of theme (prayers to God in times of trouble), and because of the name mentioned in the subscription. Psalms 42, 44-49, 84-85, and 87-88 mention the Korahites. Korah, the chief of the clan of Edom, is listed as both the son of Esau (Genesis 36:5, 14; I Chronicles 1:35), and the grandson of Esau, son of Eliphaz (Genesis 36:16). For reference, the superscriptions of 73 psalms mention David. The Korahites were one of the major guilds of Temple singers (II Chronicles 20:19), and are also mentioned as Temple gatekeepers (I Chronicles 9:19; 26:1; 19) and bakers (I Chronicles 9:31).
Many scholars divide the Psalter into five books. Note that Psalm 41 ends with a benediction, similar to those found in Psalms 72:19, 89:52, and 106:48. These five books of the Psalter are thought to mirror the five books of Moses, the Pentateuch: Genesis, Exodus, Leviticus, Numbers, and Deuteronomy.
This information comes from The New Interpreter’s Bible, Volume IV, and the HarperCollins Bible Dictionary, both resources from our church library!