It is known that the body has three kinds of carnal movements.
The first is a natural movement, inherent in it, which does not produce anything (sinful, burdening the conscience) without the consent of the soul and merely lets it be known that it exists in the body.
The second kind of movement in the body is produced by too abundant food and drink, when the resulting heat in the blood stimulates the body to fight against the soul and urges it towards impure lusts. Wherefore the Apostle says : ‘be not drunk with wine, wherein is excess’ (Eph. v. 18). In the same way the Lord commands His disciples in the Gospels : ‘take heed to yourselves, lest at any time your hearts be overcharged with surfeiting, and drunkenness’ (Luke xxi. 34). And those who are monks, and are zealous to achieve the full measure of sanctity and purity, should take particular care always to keep themselves such that they can say with the Apostle, ‘I keep under my body, and bring it into subjection’ (i Cor. ix. 27).
The third movement comes from the evil spirits, who thus tempt us out of envy and try to weaken those who have found purity (who are already monks), or to lead astray from the path those who wish to enter into the door of purity (that is, those who are as yet on the threshold of monkhood).
Saint Anthony the Great