"Then he brought me back to the outer gate of the sanctuary, which faces east; and it was shut. And he said to me, 'This gate shall remain shut; it shall not be opened, and no one shall enter by it; for the LORD, the God of Israel, has entered by it; therefore it shall remain shut.'"
This passage from Ezekiel is a favorite for the Church Fathers in defense of the Blessed Virgin Mary's perptual virginity.
"Some quite emphatically understand this closed gate through which only the Lord God of Israel passes....as the Virgin Mary, who remains a Virgin before and after childbirth. In fact, she remains always a Virgin. in the moment in which the Angel speaks with her and when the Son of God is born." -St. Jerome
"she is closed because she is a virgin; she is a gate, because Christ has entered through her......This gate faces east, because she has given birth to him who rises, the sun of justice.....Mary is the good gate that was closed and was not opened. Christ passed through it, but did not open it." -St. Ambrose
"[Christ] precisely as Legislator fulfills His own law in a manner transcending that law: He does not in fact open, but leaves closed the virginal gate, removes not the natural seal, injures not the Mother of God, but leaves intact her virginal honor." -Hesychius of Jerusalem
"[Jesus] as God does not break the virginal seals: in such wise He exits the womb as He entered there through the ear; thus He was born, as He was conceived: without passion He entered, without corruption He exited, according to the Ezekiel who says: 'This gate will remain closed.'" -St, Proclus of Constantinople