The Predestination of the Saints/Gift of Perseverance

Certainly, when the apostle says, “Therefore it is of faith that the promise may be sure according to grace,” I marvel that men would rather entrust themselves to their own weakness, than to the strength of God's promise. But do you say, God's will concerning myself is to me uncertain? What then? Is your own will concerning yourself certain to you? And do you not fear—“Let him that thinks he stands take heed lest he fall”? Since, then, both are uncertain, why does not man commit his faith, hope, and love to the stronger will rather than to the weaker?