10 Timothy then, being aware of all these things, fortified himself on every side; for he knew that youth is an age of difficulty; that it is unstable; easily deceived; very apt to slip; and requires an exceedingly strong bridle. It is indeed a sort of combustible pile easily catching anything from without, and quickly kindled; and for that reason he took care to smother it on all sides; and strove to abate the flame in every way. The steed that was unmanageable and restive he curbed with much vehemence, until he had tamed him of his wanton tricks; until he had made him docile; and delivered him under entire control, into the hands of that reason which is the charioteer. “Let the body,” says he, “be infirm; but let not the soul be infirm; let the flesh be bridled; but let not the race of the spirit towards heaven be checked.”
But moreover, one might especially wonder at the man for this, that being thus diseased, and struggling with such an infirmity, he did not become indifferent to God's business, but flew everywhere faster than those who have sound and vigourous constitutions; now to Ephesus; now to Corinth; often to Macedonia and Italy; appearing everywhere, by land and by sea, with the Teacher, sharing in everything his struggles and continuous dangers; while the spiritual wisdom of his soul was not put to shame by his bodily infirmity.
Such a thing is zeal for God! such lightness of wing does it impart! For as with those who possess well-regulated and sound constitutions, strength is of no avail, if the soul is abject, slothful, and stupid; so with those who are reduced to extreme weakness, no hurt arises from their infirmity, if the soul be noble and well awake.
Source: Homilies on the Statues (New Advent)