Saint Remigius: " Be it known moreover, that as this precept respecting endurance under persecution specially belongs to the Apostles and their successors, men of fortitude, so the permission to fly is sufficiently proper for the weak in the faith, to whom the tender Master condescends, lest if they should offer themselves for martyrdom, under the pain they should deny the faith; and the sin of flight is lighter than that of denial.
This decree by Saint Remigius states that as endurance in persecution is a hallmark of the Apostles and their successors, individuals of great fortitude, so the permission to fly is an apt fit for those who lack such resolve, to whom the compassionate Master shows mercy, lest they deny their faith if offered martyrdom; and the sin of fleeing is less severe than that of denying.