It is clear that this knowledge [of his death] must somehow have been withdrawn from Him before He praed in Gethsemane. He could not, with whatever reservation about the Father's will, have prayed that the cup might pass and simultaneously known that it rould would not. That is both a logical and psychological impossibility. You see what this involves? Lest any trial incident to humanity should be lacking, the torments of hope - of suspense, anxiety - were at the last moment loosed upon Him - the supposed possibility that, after all, He might, He just conceivably might, be spared the supreme horror. There was precedent. Isaac had been spared: he too at the last moment, he also against all apparent probability.... But for this last (and erroneous) hope against hope, and the consequent tumult of the soul, the sweat of blood, perhaps He would not have been very Man. To live in a fully predictable world is not to be a man.

C.S. Lewis. Joyful Christian, 171-72 as quoted in Tad R. Callister, The Infinite Atonement. 2000. p. 112