I find great comfort in the fact that because of the incarnation of Christ, God is forever bound to man.  God cannot be bound by anything outside of Himself, but in Jesus Christ, God united Himself to humanity forever in the personal union on humanity and deity.  The eternal Logos, the Second Person, the Word of God, took a full human nature, body and soul, and thus I can know with certainty that God can never give up on humanity, for He is personally united to humanity, irrevocably, forever.  So He will certainly finish the work of salvation that He started.  His Word that He would do so is of course sufficient, but the incarnation makes that promise visible and concrete.