John Milton is really God.Ok we have Kevin doing everything he can to win his cases. We see where his life goes if he continues onto this path. We even see him giving Kevin a second chance in the end. If that isn't divine intervention I don't know what is.
All of the cases are planned and engineered by John Milton himself.That Mexican he spoke with in the tube will likely kill his wife and his friend. Then, one of Milton's lawyers will protect him in the court. It's not a big stretch of imagination that all Kevin's cases were inspired by Devil's guidance, too. That way, Milton establishes a vicious circle - he makes people commit sins and makes his lawyers commit sins by saving people, who have committed sins, from judgment.
Al Pacino wasn't really acting.He really is the Devil.
Some of Milton's other children have appeared in other filmsNamely, Top Dollar and his sister, Myca. It would explain the incest.