Thou hast given him his heart's desire - This seems to refer to the prayers offered in the preceding Psalm; see especially Psalm 21:1-4.
Thou hast given him his heart‘s desire - See the notes at Psalm 20:4. This had been the prayer of the people that God would “grant him according to his own heart, and fulfil all his counsel,” and this desire had now been granted. All that had been wished; all that had been prayed for by himself or by the people, had been granted.
And hast not withholden - Hast not denied or refused.
The request of his lips - The request, or the desire which his lips had uttered. The meaning is, that his petitions had been filly granted.
Selah - See the notes at Psalm 3:2.