Buddha, the Prequel: Vessantara Gives Away His Children and His Wife

In the penultimate human life of the series which ended with our Buddha, Siddhattha Gotama, Prince Vessantara gives away the state elephant; he is banished from the city and goes to live in a forest with his wife and children. He gives the children away as servants to a vile old beggar, then his wife (to the King of the Gods in disguise). This is often presented as his fulfilling the Perfection of Generosity. What sense can we make of this?