All this is, is an indicative statement about those who had already believed! The verbs are all present, indicative, active, not passive, meaning that the sheep are acting of their own accord for their own benefit. There is nothing to imply that there are a select group of people who alone are chosen!
We are not put into a position "to decide to make God's work effectual"; the atonement has effected all that it was meant to accomplish. The atonement makes it possible for God to extend grace to man instead of wrath because of Christ's death. This is accomplished regardless of our decision. The scapegoat, however, cannot be set free to carry away our sins until we confess our sins upon his head, that is confess to Christ that we have sinned against him, and that we believe that he has died for our sins and will carry them away never to be remembered again!
Christ's atonement is not ever ineffectual, it has done all that it was meant to do. Whether we believe in what he has done or not does not change the fact that God has been reconciled to the world, that wrath has been turned away and that the extension of grace is now possible, and that whosoever believes will be saved! Christ has accomplished all of this, and it is finished! My benefiting from it what he has finished doesn't make it unfinished!
Doug