John Gill Commentary Psalms 21:2

"Thou hast given him his heart`s desire, And hast not withholden the request of his lips. Selah" — Psalms 21:2 (ASV)

You have given him his heart's desire
Which the church had prayed for in (Psalms 20:4) ; whatever Christ's heart desired, or his lips requested, has been given him;

and have not withheld the request of his lips .
Whatever he asked in the council and covenant of peace was granted; he asked for all the elect, as his spouse and bride; these were the desire of his heart and eyes, and they were given him; he asked for all the blessings of grace for them, and all grace was given to them in him; he asked for glory, for eternal life, and it was promised him; and not only the promise of it was put into his hand, but the thing itself; see (Psalms 2:8) (2 Timothy 1:1 2 Timothy 1:9) (1 John 5:11) ; and (Psalms 20:4) ;

whatever he requested of his Father, when here on earth, was granted; he always heard him; that memorable prayer of his in (John 17:1–26) is heard and answered, both in what respects himself, his own glorification, and the conversion, sanctification, union, preservation, and glorification of his people; whatever he now desires and requests in heaven, as the advocate and intercessor for his saints, is ever fulfilled; which is an instance of the great regard Jehovah has unto him, and may be considered as a reason of his joy in him.

Selah; on this word, (See Gill on Psalms 3:2).