John Gill Commentary Psalms 20:4

"Grant thee thy heart`s desire, And fulfil all thy counsel." — Psalms 20:4 (ASV)

Grant you according to your own heart
Which is to see his seed, the travail of his soul, and to have the pleasure of the Lord prosper in his hand; to have all his people called, preserved, and glorified;

and fulfil all your counsel ;
whatever was agreed upon in the council and covenant of peace between him and his Father, relating to his own glory, and the salvation of his people.