Musar על סוכה 75:18

The first subdivision of the first division, namely, piety in deed between man and G-d, its matter is for a person to fulfill the mitzvot in all their fine details to the furthest extent of one's ability. Our sages, of blessed memory, called these "the remnants of a mitzva". They said: "the remnants of the mitzvot prevent divine punishment" (Sukkah 38a). For even though the body of a mitzvah is fulfilled without them and one has already discharged his obligation, nevertheless, this is sufficient for the general masses of the Jewish people. But those who are Pious must only increase fulfillment in the mitzvot and not omit any detail whatsoever of them.