Theophylact of Ohrid, on 1Thess 3:10

“Night and day more abundantly praying that we may see your face, and may accomplish those things that are wanting to your faith?”

“If above he testified to their "standing," then how does he now say: "what was lacking in your faith"? They did not benefit from all the teaching, and they were lacking, perhaps, knowledge about the resurrection and other similar matters. Also, there were many false teachers, which is why he said: "what was lacking." Where he feared for the faith itself, he says: "we sent Timothy to establish you" (v. 2); but here he says: "to supply," which pertains more to teaching than to establishing. For we call imperfect that which lacks only a little.”

Imported from an open dataset — not yet checked against the printed edition.