Musar su Salmi 12:7

This is what king David, peace be unto him, said: "Whom have I in Heaven [but you]? And having You I desire none on earth" (Tehilim 73:25), and likewise "your Word is very pure; therefore your servant loves it" (Tehilim 119:140). For in truth, the true divine service must be purified far more than gold and silver. This is what was said regarding the Torah: "the Words of G-d are pure words, like silver refined in a furnace on the earth, purified seven times" (Tehilim 12:7).

Then let him contemplate what he is going to do and before Whom he is going to do it. For when he enters in this contemplation, it will be easy for him to cast away external motives, and to implant in his heart the true and desirable motive.