Hilary of Poitiers

Otherwise; He says not, Let this cup pass away from Me, for that would be the speech of one who feared it; but He prays that it may pass not so as that He should be passed over, but that when it has passed from Him, it may go to another. His whole fear then is for those who were to suffer, and therefore He prays for those who were to suffer after Him, saying, Let this cup pass from me, i. e. as it is drunk by Me, so let it be drunk by these, without mistrust, without sense of pain, without fear of death. He says, If it be possible, because flesh and blood shrink from these things, and it is hard for human bodies not to sink beneath their infliction. That He says, Not as I will, but as thou wilt, He would fain indeed that they should not suffer, lest their faith should fail in their sufferings, if indeed we might attain to the glory of our joint inheritance with Him without the hardship of sharing in His Passion. He says, Not as I will, but as thou wilt, because it is the Father’s will that strength to drink of the cup should pass from Him to them, that the Devil might be vanquished not so much by Christ as by His disciples also.