Ellicott's Commentary On The Whole Bible
Psalms 21 - Introduction
XXI.
The preceding psalm was a prayer for success; this is a thanksgiving after victory. Possibly, as many think, the two refer to the same event, and are by the same author. The composition is also similar, since here also the arrangement is for a part song. The people — probably a chorus of maidens (see Note to Psalms 21:3), or of Levites — meet the returning hero, with their shouts of praise to Jehovah (Psalms 21:1). The monarch himself is then addressed, perhaps by the leader of the procession (Psalms 21:8), and the whole concourse again unite in a burst of praise to God at the end. The rhythm is weak and ill-sustained.