Did the order of the Psalms follow no plan or purpose?

There is plan and purpose to the order of the Psalms, though we might not always know what it is. The same applies to books such as Isaiah.

In some cases, the commentaries reveal to us why individual Psalms are positioned where they are. The following example is excerpted from the Talmud (Berakhot 10a):

A certain non-believer said to Rabbi Abbahu: It is written "A Psalm of David when he fled from

Absalom his son" (3:1), and it is also written "A mikhtam of David when he fled from Saul in

the cave" (57:1)...Did not the event of Saul happen first? Then why did he not write it (place its position among the Psalms) first? Rabbi Abbahu replied: For you, who do not derive interpretations from juxtaposition (in the Prophets), there is a difficulty, but for us (Jews) who do derive interpretations from juxtaposition there is no difficulty....Why is the chapter of Absalom juxtaposed to the chapter of Gog and Magog (2:1)? So that if one should say to you "Is it possible that a servant (the nations) would rebel against his master (God)?" you can reply to him: Is it possible that a son would rebel against his father? Yet this happened (Absalom did this); and so this too [will happen].

See also:

More about the Psalms