"Do not speculate beyond the text. Do not require of it something more than what it simply says. Do not ask, 'But precisely how was it that the Spirit accomplished this in a virgin?' For even when nature is at work, it is impossible fully to explain the manner of the formation of the person. How then when the Spirit is accomplishing miracles, shall we be able to express their precise causes?"
St. John Chyrysostom, The Gospel of Matthew, Homily 4.3