If these thoughts [being disturbed by the idea of predestination] come to the mind, and only useless efforts are made to dispel them, they must end in causing us to abandon ourselves completely to God, assured that it is infinitely better to leave our salvation in His hands than to rely on our own strength. Only by thus doing shall we find peace. The whole doctrine of the divine Master's secret is that we must adore Him and not claim to fathom Him. We must lose ourselves in this impenetrable height and depth of divine wisdom and plunge ourselves as if lost in His immense goodness, though expecting everything from Him, without however relaxing our efforts, which He demands from us for our salvation.
Jacques-Bénigne Bossuet (quoted in “Predestination”, by Reginald Garrigou-Lagrange O.P.)