Church Fathers on Luke 9:21

Our Lord having retired from the multitude, and being in a place apart, was engaged in prayer. As it is said, And it came to pass, as he was alone praying. For He ordained Himself as an example of this, instructing His disciples by an easy’ method of teaching. For I suppose the rulers of the people ought to be superior also in good deeds, to those that are under them, ever holding converse with them in all necessary things, and treating of those things in which God delights.

Now the disciples were with the Lord, but He alone prayed to the Father, since the saints may be joined to the Lord in the bond of faith and love, but the Son alone is able to penetrate the incomprehensible secrets of the Father’s will. Every where then He prays alone, for human wishes comprehend not the counsel of God, nor can any one be a partaker with Christ of the deep things of God.

Now it may raise a question, that Luke says that our Lord asked His disciples, Whom do men say that I am? at the same time that He was alone praying, and they also were with Him; whereas Mark says, that they were asked this question by our Lord on the way; but this is difficult only to him who never prayed on the way.