For thou preventest him with the blessings of goodness: thou settest a crown of pure gold on his head. Thou preventest him - To prevent, from prcevenio, literally signifies to go before. Hence that prayer in the communion service of our public Liturgy, "Prevent us, O Lord, in all our doings, with thy most gracious favor!" That is, "Go before us in thy mercy, make our way plain, and enable us to perform what is right in thy sight!" And this sense of prevent is a literal version of the original word תקדמנו tekademennu. "For thou shalt go before him with the blessings of goodness."
Our ancestors used God before in this sense. So in Henry V.'s speech to the French herald previously to the battle of Agincourt: -
"Go therefore; tell thy master, here Iam.
My ransom is this frail and worthless trunk;
My army, but a weak and sickly guard:
Yet, God before, tell him we will come on,
Though France himself, and such another neighbor,
Stand in our way."
A crown of pure gold - Probably alluding to the crown of the king of Rabbah, which, on the taking of the city, David took and put on his own head. See the history, 2 Samuel 12:26-30 (note).