We mentioned that betrothal can be done with money. Why is that so? Furthermore, there is a related law that a father can give his daughter away in marriage when she is young, and in that case the money that the groom pays goes to the father.
Both questions have the same, if non-trivial answer. This is derived from the law of a Jewish slave-girl, here is how. The father can sell his daughter as a servant. In this case, it is understood that when she grows up the buyer will take her as a wife, or designate her for her son. If none of these happen, then she goes out free, and the Torah adds, “no money!” We already know that “free” means “no money”. So we understand that it is in this case that there is no money, but in another related case there is money. And when is it? When a woman gets married, or when the father gives her away in marriage.
That is exactly what we wanted to demonstrate, that the betrothal which will lead to marriage (chuppah) can be done with money.
Today both events happen under the chuppah in close succession: first the groom gives money (or a ring) to the bride, then the ceremony is concluded under the chuppah, which symbolizes the new home.
Art: Man in a Smock by Gustave Caillebotte