Statements related to Yibbum beyond matters of law
The ideal was originally yibbum, and chalitzah was only if yibbum would not be done, until men started to perform yibbum for non-altruistic motives: Ketuvot 64a; Bechorot 13a
If one marries his sister-in-law for non-altruistic motives, it is like marrying incestuously: Yevamot 109a
Tehillim 128:6 says, "See children for your children, peace upon Israel." When one has grandchildren, so that his children will not need to worry about yibbum and chalitzah, then there is peace upon Israel: Ketuvot 50a
