Why is it encouraged in the torah to marry a niece?
Answer:
The Gemara (Yevamos 62b; Sanhedrin 76b) writes that it is good to marry one’s niece, and Otzar Ha-Geonim (Yevamos 62a, no. 333) mentions that this is a “mitzvas rabbanim.” The reason behind it appears to be because of the maxim of being close with one’s family, and Rashi cites the verse “You shall not ignore your flesh.” Marrying “in the family” strengthens family ties, and ensures the closeness of family members who are liable to become distant.
Some add reasons for the practice based on Kabbalah.
