9 For often by means of these members of our bodies, God illustrates for us the method of His own operations, enlightening our intelligence by using terms commonly understood: as when He says, Whose hands created all the host of heaven; or again, The eyes of the Lord are upon the righteous; or again, I have found David, the son of Jesse, a man after My own heart. Now by the heart is denoted the desire, to which David was well-pleasing through the uprightness of his character; and knowledge of the whole universe, whereby nothing is beyond God's ken, is expressed under the term 'eyes;' and His creative activity, whereby nothing exists which is not of God, is understood by the name of 'hands.'
Therefore as God wills and foresees and does everything, and even in the use of terms denoting bodily action must be understood to have no need of the assistance of a body; surely, now, in the statement that He begot from the womb, the idea is brought forward not of a human origin produced by a bodily act, but of a birth which must be understood as spiritual, since in the other cases where members are spoken of, this is done to represent to us other active powers in God.
Source: On the Trinity (New Advent)