In Mesachtah Kiddushin 29a, the Gemarah states that a woman is excluded from the the Mitzvah of circumcizing her son as the Pasuk says Avraham performed this mitzvah " ka'asher tzivah oisoi " as Hashem commanded HIM. Meaning, only Avraham as a male was commanded, but not Sarah.
Tosafos asks, why it is needed to have this drashah don't we already know that women are exempt from all mitzvos aseih shehazman gramah - positive commandments that have time restraints?
Tosafos offers an explanation according to those who hold that a delayed bris may be performed at any time. This would redefine it as a mitzvah without a time limit, and, if not for the drashah metioned earlier a woman would be included in the mitzvah. Therefore the pasuk, "ka'asher tzivah oisoi" is needed to exclude them.
There is another possible answer which can apply even according to those who hold that a delayed bris may not be done at night.
When a bris takes place on the 8th day, it is quite obvious that the mitzvah is the actual circumcision which taking place. That is very well understood as a finite and time defined mitzvah. However, when the bris takes place at another time, a new facet of the mitzvah is exposed. There is a general responsibility placed upon the parent to ensure the child has a bris. That responsibility is not limited by any time restraint at all. Only the actual circumcision is bound to the daytime hours. But the planning, arranging, and reservation of a mohel etc. has no specific time.
Therefore if not for the above drashah there would be room to say that a woman IS commanded to circumcize her son, as a general administrator of the bris! This, as we said is not a time-specific mitzvah but rather a constant requirement to bring about the circumcision. That is why the extra drashah of "ka'asher tzivah oisoi" is needed to exempt women from this as well.
This displays the dual role a parent has in his Judaism. On the one hand there are the private duties, as a human being, created by Hakadosh Baruch Hu, and chosen to do His will. On the other hand, a parent is a public official, sworn into office to disseminate, educate, and train another generation of G-D loving, and G-D fearing, dedicated jews.
This transition is apparent in this weeks parshah (vayechi) as well. As we see the changeover of the shvatim from being children of yaakov to becoming the leaders of the klall yisrael in their first galus. One of the major steps taken then, was the pact and promise to always retain their jewish names and as we know this remained a z'chus for their redemption many years later.
This delayed bris brings to mind the transition that a father goes through upon the birth of a son. He is not just another person fulfilling his own private duties in avodas Hashem, with his child being the object for the act of his mitzvah. The father now has a new responsability in becoming a link in our Mesorah. He becomes an AVI HaBEN - a complete spiritual caregiver for the next generation. This usually requires a new dedication to the improvement of the father's own avodas Hashem as he accepts his new lofty position in klal yisrael.
