Actually, I'm not big on the idea of the Father running forward. I object not so much to the stillness of the Father as to the stark, static quality which is a feature of many productions (including those by Miami City Ballet, directed by one of the greatest of Prodigals, Edward Villella).
The Rembrandt painting linked by kfw captures what I'm think the part needs. It does depict a moment of perfect stillness. But the father's face, as well as the positioning of his hands, has gentleness, sadness, consolation ... in other words, life. The Prodigal can't perform this big climactic moment in a vacume. He needs a father who is experiencing and depicting feelings of equivalent weight.
Shaun O'Brien, in the early NYCB performances, certainly conveyed much of what you see in the Rembrandt without altering the choreography or violating the music. It was a great stage performance. Other less talented dance-actors don't always handle it quite as well.
Sorry to keep this thread so Off Topic. Thanks, AnthonyNYC, for bringing us back to the Siren. So please: let's have more Siren sightings, Siren critiques, and Siren theories?