Church Fathers on Matthew 26:39

He took with Him the self-confident Peter, and the others, that they might see Him falling on His face and praying, and might learn not to think great things, but little things of themselves, and not to be hasty in promising, but careful in prayer. And therefore, 'He went forward a little,' not to go far from them, but that He might be near them in His prayer.

Whence He says emphatically, 'This cup,' that is, of this people of the Jews, who, if they shall put Me to death, can have no excuse for their ignorance, seeing they have the Law and the Prophets, who speak of Me.

And that none might think that He limited His Father’s power, He said not, 'If thou canst do it,' but 'If it may be,' or, 'If it be possible;' as much as to say, If thou wilt. For whatever God wills can be done, as Luke expresses more plainly; for he says not, 'If it be possible,' but 'If thou wilt.'