John Trapp on Psalms 40:9

Verſ. 9. I have preached righteouſneſs in the great congregation] David did this, but Chriſt much more by the everlaſting Goſpel, ſent the whole world throughout: great was the company of Preachers, and large was their commiſſion. See a draught of it, Acts 26.18.

I have declared thy faithfulneſs, and thy ſalvation] Righteouſneſs of Chriſt imputed, faithfulneſs of God in fulfilling his Promiſes, Salvation the end of faith, loving kindneſs and truth the ground of all the former, Gods loving kindneſs, or mercy moving him to promiſe, and his truth binding him to perform; theſe are thoſe Pearls that Chriſt by his Preachers caſteth before people, if they bee but as forward to take them, as he is to tender them: How beautiful ſhould the feet be of thoſe that bring ſuch glad tidings? and how heavie will the duſt of ſuch feet bee, ſhaken off againſt deſpiſers?

O Lord them knoweſt] ſc. That I have herein done mine utmoſt, and with an upright heart.