ISB ~ 2 Thessalonians 3 v10

when we were … with you:Suggests idleness was already an issue when Paul ministered among them. This is why his earlier letter urges the Church to “admonish the idle” (1 Thess 5:14).

let him not eat:i.e., let him not live off the labor of others without contributing efforts of his own.

• Manual labor aims at obtaining food, removing idleness, curbing fallen desires, and enabling almsgiving. As a means of acquiring food, work is commanded as a precept, so that one who has no other means of livelihood is bound to work. This is signified by the words of the apostle (St. Thomas Aquinas, Summa Theologiae II-II, 187, 3).