Offer to Christ the labours of your youth, and in your old age you will rejoice in the wealth of dispassion. What is gathered in youth nourishes and comforts those who are tired out in old age.
In our youth let us labour ardently and let us run vigilantly, for the hour of death is unknown. We have very evil and dangerous, cunning, unscrupulous foes, who hold fire in their hands and try to burn the temple of God with the flame that is in it. These foes are strong; they never sleep; they are incorporeal and invisible.
Let no one when he is young listen to his enemies, the demons, when they say to him: ‘Do not wear out your flesh lest you make it sick and weak.’ For you will scarcely find anyone, especially in the present generation, who is determined to mortify his flesh, although he might deprive himself of many pleasant dishes. The aim of this demon is to make the very outset of our spiritual life lax and negligent, and then make the end correspond to the beginning.
[John Climacus, Ladder of Divine Ascent]