“For the Son of man is as a man taking a far journey, who left his house, and gave authority to his servants, and to every man his work, and commanded the porter to watch.”
It's like a man going away: he leaves his house and puts his servants in charge, each with their assigned task, and tells the one at the door to keep watch — the parable of the absent householder provides the framework for the disciples' situation. The householder has departed (Jesus, by his death and resurrection/ascension), left servants in charge (the disciples with the kingdom mission), each with their task (specific callings), and the doorkeeper must keep watch (the general vigilance of the whole community).
Church Fathers on Mark 13:34
The Lord wishing to prevent His disciples from asking about that day and hour, says, 'But of that day and that hour knoweth no man, no, not the angels which are in heaven, neither the Son, but the Father.'
This ignorance of the day and hour is urged against the Only-Begotten God, as if, God born of God had not the same perfection of nature as God. But first, let common sense decide whether it is credible that He, who is the cause that all things are, and are to be, should be ignorant of any out of all these things. For how can it be beyond the knowledge of that nature, by which and in which that which is to be done is contained? And can He be ignorant of that day, which is the…
For we must needs watch with our souls before the death of the body.