God gives the faith to believe. You do the believing. God doesn't do your believing for you. He gives you the power for you to choose to believe, if you want to believe. The believing/ trusting part is up to you. Will you choose to trust him and continue to trust him and be saved? Or will you reject the power of faith he gives for you to believe and choose not to believe and be saved? You must choose to believe and continue to believe in order to be saved when Jesus comes back. Those who turn back will not be heirs along with the sons of God.