This the Baal Shem Tov teaches from Pirkei Avot הוי זהיר במצוה קלה כבחמורה - one should be diligent in a simple mitzwah as one is with a serious mitzwah. He reads this a little differently, One should be illumined by a simple mitzwah as one is illumined with a serious mitzwah.
He goes on to say that from this we will be forever watchful throughout the day lest we miss out on mitzwah. (Which seems very different than what he first said, that we should be careful to perform at least one mitzwah, big or small, a day.)
(paraphrased from Tzava'at HaRivash)
Here's what I think one can take away from this teaching: Often mitzwoth are performed half-heartedly, which creates only half-hearted angels, and creates only a minor illumination. Everyone is presented each day with the unique oppurtunity to perform a mitzwah whole-heartedly and in so doing, 1) create a pure angel to fight on our behalf in any supernal judgements, and 2) shine with the true light of the Torah (כי נר מצוה ותורה אור - because a mitzwah is a candle and the Torah its light.)
Each day it is within our grasp to create such an angel and to light such a fire. Knowing this will inspire us to examine all of our daily interactions, perform all the mitzwoth that come to our hand, just so as not to miss out on this unique oppurtunity.
May we all shine with the light of Torah in all of our mitzwoth.