The Torah verse "If another he take for him" (Exodus 21:10) is read by the Mekhilta as the source for a surprising obligation. From this verse, the Sages ruled that a father is obligated to marry off his young son while the son is still under his care. The connection between the verse about a master taking another wife and a father's duty to arrange his son's marriage requires explanation.
The Mekhilta links this ruling to another verse: "And you shall make them known to your sons and to your sons' sons" (Deuteronomy 4:9). This passage commands the transmission of Torah knowledge across generations. The Mekhilta asks a practical question about this command. When does a person merit seeing his sons' sons? When does a man live long enough to teach his grandchildren?
The answer is startlingly direct: when you marry off your sons while they are young. If a father waits too long to arrange his son's marriage, the generational chain stretches out. The grandfather may not live to see the grandchildren who are supposed to receive his teaching. But if the father acts early, marrying off his son while the son is still "small" (still under the father's authority and care), the generations compress. The grandfather lives to see and teach his grandchildren. The commandment to transmit Torah across three generations becomes physically possible.
This passage connects two seemingly unrelated obligations, marital duty and Torah transmission, into a single practical framework. The father who arranges his son's marriage is not merely fulfilling a social convention. He is creating the conditions necessary for the Torah's own command to be fulfilled. Early marriage makes multi-generational teaching possible. Delay makes it impossible. The obligation to marry off one's children is ultimately an obligation to ensure the survival of Torah knowledge.