John 20:19

Since then it was likely that the disciples on hearing these things would either not believe the woman, or, believing, would grieve that He had not deemed them worthy of the vision, though He promised to meet them in Galilee; in order that they might not by dwelling on this be unsettled, He let not a single day pass, but having brought them to a state of longing, by their knowledge that He was risen, and by what they heard from the woman, when they were thirsting to see Him, and were greatly afraid, (which thing itself especially made their yearning greater,) He then, when it was evening, presented Himself before them, and that very marvelously. And why did He appear in the "evening"? Because it was probable that they would then especially be very fearful. But the marvel was, why they did not suppose Him to be an apparition; for He entered, "when the doors were shut," and suddenly. The chief cause was, that the woman beforehand had wrought great faith in them; besides, He showed His countenance to them dear and mild. He came not by day, in order that all might be collected together. For great was the amazement; for neither did He knock at the door but all at once stood in the midst, and showed His side and His hands. At the same time also by His Voice He smoothed their tossing thought, by saying, "Peace be unto you." That is, "Be not troubled"; at the same time reminding them of the word which He spake to them before the Crucifixion, "My peace I leave unto you"; and again, "In me ye have peace, but in the world ye shall have tribulation."

(Serm. cx. et cl. Pasch. aliquid simile.) Some are strongly indisposed to believe this miracle, and argue thus: If the same body rose again, which hung upon the Cross, how could that body enter through shut doors? But if thou comprehendest the mode, it is no miracle: when reason fails, then is faith edified. (Tr. cxx) The shut door did not hinder the body, wherein Divinity resided. He could enter without open doors, who was born without a violation of His mother's virginity.

"Mary Magdalene came and told the disciples, I have seen the Lord, and He hath spoken these things unto me. Then the same day at evening, being the first day of the week, when the doors were shut where the disciples were assembled for fear of the Jews, came Jesus, and stood in the midst, and saith unto them, Peace be unto you. And when He had so said, He showed unto them His hands and His side." For nails had pierced His hands, a spear had laid open His side: and there the marks of the wounds are preserved for healing the hearts of the doubting. But the shutting of doors presented no obstacle to the matter of His body, wherein Godhead resided. He indeed could enter without their being opened, by whose birth the virginity of His mother remained inviolate.

Wherein is shown the infirmity of the Apostles. They assembled with doors shut, through that same fear of the Jews, which had before scattered them: Came Jesus, and stood in the midst. He came in the evening, because they would be the most afraid at that time.

Or because He waited till all were assembled: and with shut doors, that he might show how that in the very same way he had risen again, i. e. with the stone lying on the scpulchre.