The Berachah On Kiddushin

Based on this we can answer the other question that we raised on the Rambam. Since the mitzvah is not merely to give a woman kiddushin (the mitzvah includes living together after kiddushin), the Rambam had to write that if one gave the woman kiddushin without reciting a berachah, he is not permitted to recite the berachah thereafter. This is because one may have thought that since the mitzvah is not yet complete one may still recite a berachah. The Rambam therefore felt the need to stress that one may not recite the berachah after he has given the kiddushin. The reason why one may not recite the berachah at that point is because although the mitzvah is not yet complete, the action aspect of the mitzvah (ma’aseh mitzvah) is complete. One may only recite a berachah on a mitzvah before the action part of the mitzvah is complete.