Abstinence is for everyone, not just for monks. Husbands and wives for whom marriage means only the satisfaction of bodily passions will not be justified. They will answer before God for not having been abstinent. Of course, as the Apostle says, they are not to abstain from each other for a long time, lest the devil deceive them, but they should abstain according to mutual consent (cf. I Cor. 7:1-6). Married people should abstain from corporeal relations during fasts and on great Feast days.
Because of the Fall of man, the natural order of things has become chaotic. In nature, there is an order for all things, but with man there is chaos, Everything is distorted and turned around. Because of our disobedience to the commandments of our Heavenly Father, we have lost the natural order. In order to reestablish this order, we must practice abstinence.