Theophylact of Ohrid

Thus, when He says, "Take this cup away from Me," He reveals in Himself the human property; but then He added, "yet not what I will, but what You will" — He teaches us, despite the demands of nature, to ask for what is pleasing to God.

Commentary on Mark ↗

Dionysius of Alexandria

And surely it is the fact that the Saviour asks neither what is impossible, nor what is impracticable, nor what is contrary to the will of the Father. It is something possible, for Mark makes mention of His saying, "Abba, Father, all things are possible unto Thee;" and they are possible if He wills them, for Luke tells us that He said, "Father, if Thou be willing, remove this cup from me." The Holy Spirit therefore, apportioned among the evangelists, makes up the full account of our Saviour's whole disposition by the expressions of …

On Luke XXII. 42, Etc. ↗

Hilary of Poitiers

Again, He does not pray that the cup may pass over Himself, but that it may pass away from Himself, though before it could pass away He must have drunk it. But, further, 'to pass away' does not mean merely 'to leave the place,' but 'not to exist any more at all:' which is shewn in the language of the Gospels and Epistles: for example, Heaven and earth shall pass away, but My word shall not perish: also the Apostle says, Behold the old things are passed away; they are become new. And again, The fashion of this world shall pass away. …

On The Trinity 10.42 ↗

Bede

But He prays, that the cup may pass away, to show that He is very man, wherefore He adds: Take away this cup from me. But remembering why He was sent, He accomplishes the dispensation for which He was sent, and cries out, But not what I will, but what thou wilt. As if He had said, If death can die, without my dying according to the flesh, let this cup pass away; but since this cannot be otherwise, not what I will, but what thou wilt. …

Catena Aurea by Aquinas ↗