Torah, Deuteronomy 25:05: If brothers reside together, and one of them dies having no son, the dead man’s wife shall not marry an outsider. [Rather,] her husband’s brother shall be intimate with her, making her a wife for himself, thus performing the obligation of a husband’s brother with her.
This is a big commandment that religious people observe even today.
From the point of view of spiritual work, “If brothers reside together, and one of them dies having no son,” meaning that the next spiritual degree was not attained, then the brother who will marry his wife (desire) should lead to it.
Question: But why should he marry her?
Torah, Deuteronomy 25:06: And it will be, that the eldest brother [who performs the levirate marriage, if] she [can] bear will succeed in the name of his deceased brother, so that his [the deceased brother’s] name shall not be obliterated from Israel.
The brother and wife of the deceased understand what they are doing when they get married—by this, they continue the soul of the deceased brother.
It means that this has nothing to do with love; they just fulfill the laws of creation. And there is not any cruelty in this; on the contrary, there is the openness and frankness that give a person a feeling of being elevated in the world, a sense of truth and verity.
From KabTV’s “Secrets of the Eternal Book” 11/2/16