Kiddushin 41 - Marriage With the Help of an Agent

A man can betroth a woman either personally or through his agent. A woman can accept kiddushin and become betrothed either personally or through her agent. A man may give his daughter in betrothal when she is a na'arah (under 12) either personally or through his agent. Performing betrothal as well as any other mitzvah personally is the preferred way.

From where in the Torah do we derive the legal concept of agency? From its use of "and he sends her" instead of a more direct "and he divorces" we learn that both man and woman can appoint an agent.