R’ Shaul Yisraeli zt”l (Siach Shaul) said: “'כל המצוה אשר אנכי מצוך היום תשמרון לעשות' - The primary desire of Hashem is that a Jew not do a mitzvah for ulterior motives but because it is a mitzvah which allows him to keep it even when he (the person) does not totally grasp the purpose of doing the mitzvah. This guarantees that he perform the entire mitzvah, not just the parts that he fully grasps.”
A Wise Man would say:
“True wisdom is like an ocean; the deeper you go the greater the treasures you’ll find.”