Albert Barnes Commentary Matthew 22:24

"saying, Teacher, Moses said, If a man die, having no children, his brother shall marry his wife, and raise up seed unto his brother." — Matthew 22:24 (ASV)

Saying, Master, Moses said, etc. Deuteronomy 25:5–6. This law was given by Moses in order to keep the families and tribes of the Israelites distinct, and to perpetuate them.

Raise up seed unto his brother. That is, the children shall be reckoned in the genealogy of the deceased brother; or, to all civil purposes, shall be considered as his.