Our Torah reading begins with the commandment of circumcision. Now, the Torah had already taught us about this mitzvah when relating the story of Abraham's circumcision. Why then does it mention it here a second time?

Our Rabbis explain that this communicates a fundamental lesson. We observe the mitzvos, not because of our Patriarchs' observance, but because we were commanded to at Sinai. Without minimizing the achievements of Abraham, Isaac, and Jacob, their Divine service merely prepares the ground for our relationship with G-d. The relationship itself is established through the giving of the Torah.

What's the difference? The Patriarchs were inspired men, trying with all the energy they could muster to reach out to G-d and establish a connection with Him. But at the giving of the Torah, G-d reached out to man.

The Patriarchs reached the highest peaks that mortals could. Their comprehension of spirituality and the love and fear they experienced represented the quintessence of man's strivings. We cannot expect to attain those heights. Nevertheless, our observance of the mitzvos possesses a measure of superiority over their Divine service. For the giving of the Torah changed the entire paradigm, lifting us above the human realm entirely. It enables us relate to G-d on His terms and tap into the spiritual potential that He grants us.

Accordingly, the commandment for circumcision - and the other commandments mentioned in the Book of Genesis - were repeated at Sinai. For this repetition enabled their observance to be charged with this superior energy.