But the ways in our life which turn aside towards sin are innumerable; and their number is told by Scripture in various manners. “Many are they that trouble me and persecute,” and “Many are they that fight against me from on high”; and many other texts like that. We may affirm, indeed, absolutely, that many are they who plot in the adulterer's fashion to destroy this truly honourable marriage, and to defile this inviolate bed; and if we must name them one by one, we charge with this adulterous spirit anger, avarice, envy, revenge, enmity, malice, hatred, and whatever the Apostle puts in the class of those things which are contrary to sound doctrine.
Now let us suppose a lady, prepossessing and lovely above her peers, and on that account wedded to a king, but besieged because of her beauty by profligate lovers. As long as she remains indignant at these would-be seducers and complains of them to her lawful husband, she keeps her chastity and has no one before her eyes but her bridegroom; the profligates find no vantage ground for their attack upon her. But if she were to listen to a single one of them, her chastity with regard to the rest would not exempt her from the retribution; it would be sufficient to condemn her, that she had allowed that one to defile the marriage bed.
So the soul whose life is in God will find her pleasure in no single one of those things which make a beauteous show to deceive her. If she were, in some fit of weakness, to admit the defilement to her heart, she would herself have broken the covenant of her spiritual marriage; and, as the Scripture tells us, “into the malicious soul Wisdom cannot come.” It may, in a word, be truly said that the Good Husband cannot come to dwell with the soul that is irascible, or malice-bearing, or harbours any other disposition which jars with that concord.
No way has been discovered of harmonizing things whose nature is antagonistic and which have nothing in common. The Apostle tells us there is “no communion of light with darkness,” or of righteousness with iniquity, or, in a word, of all the qualities which we perceive and name as the essence of God's nature, with all the opposite which are perceived in evil. Seeing, then, the impossibility of any union between mutual repellents, we understand that the vicious soul is estranged from entertaining the company of the Good.
What then is the practical lesson from this? The chaste and thoughtful virgin must sever herself from any affection which can in any way impart contagion to her soul; she must keep herself pure for the Husband who has married her, “not having spot or blemish or any such thing.”
Source: On Virginity (New Advent)