2 But what is this, and why do I foolishly importune you again? Away with entreaties, an end to coaxing words. Offended love does well to be angry. You have spurned my petition; perhaps you will listen to my remonstrance. What keeps you, effeminate soldier, in your father's house? Where are your ramparts and trenches? When have you spent a winter in the field? Lo, the trumpet sounds from heaven! Lo, the Leader comes with clouds! He is armed to subdue the world, and out of His mouth proceeds a two-edged sword to mow down all that encounters it.
But as for you, what will you do? Pass straight from your chamber to the battlefield, and from the cool shade into the burning sun? Nay, a body used to a tunic cannot endure a buckler; a head that has worn a cap refuses a helmet; a hand made tender by disuse is galled by a sword-hilt. Hear the proclamation of your King: “He that is not with me is against me, and he that gathers not with me scatters.” Remember the day on which you enlisted, when, buried with Christ in baptism, you swore fealty to Him, declaring that for His sake you would spare neither father nor mother.
Lo, the enemy is striving to slay Christ in your breast. Lo, the ranks of the foe sigh over that bounty which you received when you entered His service. Should your little nephew hang on your neck, pay no regard to him; should your mother with ashes on her hair and garments rent show you the breasts at which she nursed you, heed her not; should your father prostrate himself on the threshold, trample him under foot and go your way. With dry eyes fly to the standard of the cross. In such cases cruelty is the only true affection.
Source: Letters (New Advent)