I don't think that there is any implication on Sophocles' part. I think it's rather direct in that the battle between fate and free will is not a contest. Fate always wins out. Sophocles creates a very compelling portrait of free will. Oedipus is not a bad man nor is he a bad king. He cares for his people, represents a man of action, provides for his family, and is concerned with his well being. In this setup, free will is shown to represent strong aspects of one's being in the world. Yet, despite his benevolent actions that have been generated by free will, he is unable to escape his destiny. His free will is so compelling that Oedipus does not even know that he is kiling his father and marrying his mother. He acts in concert with sincerity that he does not even fully grasp the totality of his actions. Yet, his fate does. His fate understands where he will go even before he does, which is why fate is presented as a dominant force in the drama. Sophocles argues that our role as human beings is to merely understand this condition. Struggle as we might, as Oedipus did, to go against it or to use our free will to defeat it, such a condition is the only certainty in this life and to understand it becomes part of our own state of being in the world, as Oedipus was forced to do at the end of the drama.