Young men on the watch for attack are not in a state for fertilizing "seed thoughts" or for turning over hard matters in their minds, and care for the state of the recipient characterizes the teaching of Christ. Men are to take heed how they hear, as well as what they hear, and are to reach full growth and shape, not from outward moulding but by living process from within. Our Lord's eye is never off His pupils, and yet visible direction hardly ever appears; He sways them by an insensible touch. A great truth is brought to life by an incident of wonder, a pregnant word is let drop, a hard parable is delivered now and then; but between whiles the disciples are left to dwell on their own thoughts, as their fishing boat sails along, or as they follow their Master among the northern hills. Our Lord is ever bent on making men thoughtful and on calling out in each the inner life which is proper to the man, and for this, tranquility, or at least frequent opportunity for quiet communing with their own thoughts, was absolutely required.
from page 190, Pastor Pastorum