How does seeking others' highest good in marriage and neighbor relationships fulfill the whole law?

Les teaches that the love Paul speaks of is not erotic love or Hollywood's idea of love; it is a love that seeks the other person's highest good. Applied to marriage, a husband and wife should always attempt to do whatever they do for the other person's highest good. Applied to neighbors, the same principle holds. Paul says that as long as we are always attempting to do the other person's highest good, we are fulfilling the whole law. Les illustrates this with young people courting or dating: if they kept the other's highest good uppermost, a young man would not try to bring a young woman into an immoral state. Les notes it becomes simple, but we cannot do this merely on the basis of commanding, because we never really grow up.