Nehemiah 4:18

And it happened from that day on, that half of the young men did the work, etc. It is to be noted that not only half of the young men did the work and the other half were prepared for war, but even those who did the work, the youths, were girded with swords. For so great is the cunning of the ancient enemy, so great is the fury of his militia fighting against the Church, that not only the preachers of truth, but also the people of God themselves must always be vigilant against his schemes and stand as if in battle array. Indeed, those who build gird their loins with swords when those who devote themselves to good works, who take care to arrange those entrusted to them in an orderly manner (that is, to place living stones in the building of the holy city fittingly), strive to restrain the flows of luxury in themselves by the keenness of the word of God. Nor should it be overlooked that when David or Solomon built that same city, nothing is reported about armed builders or adversaries attacking; but when the city was destroyed due to their sins, it was rebuilt with greater labor and industry, because such is the spiritual building that pertains to the salvation of souls, that in baptism, reborn through faith and the confession of the Holy Trinity, we become his city and house by the grace of God without any of our labor. And if after the washing of the sacred font, we relapse into sins, seduced by the devil, and the enemy, victorious, destroys the walls of our virtues with the fire of vices, we must repair the buildings of good works we have lost with greater efforts of prayer, affliction, vigils, alms, and a stricter way of life. For it is more difficult for those who have experienced the allurements of vice to abstain from them than for those who are ignorant of them; and it is less laborious to beware of the unknown pleasure of the flesh than to reject the known one.