Christians are often likened to an army: we sing "Onward Christian Soldiers" and read, "Put on the whole armor of God." Imagine Christ reviewing the troops, who are supposed to be fresh and ready for battle. But some have fairly recent wounds, nicks in their armor, arms in slings, casts, etc.
He asks, "What's the matter here? Why are they wounded already?"
"Oh, they've been fighting in the barracks again."