The "father and mother", which a man is supposed to leave (as in Genesis 2:24, and Matthew 19:4, 5) are, in a spiritual sense, his proprium of will, and proprium of understanding. We all love a mixture of good and evil things, as we're growing up, and we all understand a mixture of true and false things, too. The things we "own", at first, are the evil loves and false ideas, and the more we get into them, the more they define us -- i.e. they are our "properties", or, to use a more Latinate term, our proprium. We have to change those -- get rid of the evil loves and false ideas, and invite good loves and true ideas from the Lord -- building a new understanding and a new will.

(Reference: Conjugial Love 194)