A Compendious View of the Christian Life
But, above all, it seems right that we turn away from the sight of women. For it is sin not only to touch, but to look; and he who is rightly trained must especially avoid them. “Let your eyes look straight, and your eyelids wink right.” For while it is possible for one who looks to remain steadfast; yet care must be taken against falling. For it is possible for one who looks to slip; but it is impossible for one, who looks not, to lust. For it is not enough for the chaste to be pure; but they must give all diligence, to be beyond the range of censure, shutting out all ground of suspicion, in order to the consummation of chastity; so that we may not only be faithful, but appear worthy of trust.
For this is also consequently to be guarded against, as the apostle says, “that no man should blame us; providing things honourable, not only in the sight of the Lord, but also in the sight of men.” “But turn away your eyes from a graceful woman, and contemplate not another's beauty,” says the Scripture. And if you require the reason, it will further tell you, “For by the beauty of woman many have gone astray, and at it affection blazes up like fire;” the affection which arises from the fire which we call love, leading to the fire which will never cease in consequence of sin.
Source: The Instructor (New Advent)