Bkvod Harav
If the mitzvah of yibum is to procreate a child in the name of the deceased brother, why wouldn't the fulfillment of the mitzvah only conclude upon the widowed wife's conception and giving birth?
If so, why the restriction of Biah Sheniah?
Kol Tuv
Daniel Sheinfil
Dear Daniel,
Yeyasher Kochacha for your insightful question regarding the Mitzvah of Yibum. As you correctly noted, the ultimate purpose of Yibum is to perpetuate the name of the deceased brother through progeny. However, the official Ma'aseh Mitzvah is carried out through the act of Bi'ah itself, regardless of whether it results in conception and birth. This is because the Torah defines the fulfillment of Yibum by the act, not by its outcome.
Regarding the restriction on Bi'ah Sheniyah, as I think you know, after the initial act of Yibum the widow becomes the Yavam's wife in all respects. Therefore, subsequent relations are considered ordinary marital relations and consequently the specific Mitzvah of Yibum does not apply.
Warm regards,
Yishai Rasowsky