9 Those evangelical precepts of peculiar sublimity which you make people who know no better believe that you obey, are really obeyed by multitudes in our communion. Are there not among us many of both sexes who have entirely refrained from sexual intercourse, and many formerly married who practise continence? Are there not many others who give largely of their property, or give it up altogether, and many who keep the body in subjection by fasts, either frequent or daily, or protracted beyond belief?
Then there are fraternities whose members have no property of their own, but all things common, including only things necessary for food and clothing, living with one soul and one heart towards God, inflamed with a common feeling of charity. In all such professions many turn out to be deceivers and reprobates, while many who are so are never discovered; many, too, who at first walk well, fall away rapidly from willfulness. Many are found in times of trial to have adopted this kind of life with another intention than they professed; and again, many in humility and steadfastness persevere in their course to the end, and are saved.
There are apparent diversities in these societies; but one charity unites all who, from some necessity, in obedience to the apostle's injunction, have their wives as if they had them not, and buy as if they bought not, and use this world as if they used it not. With these are joined, in the abundant riches of God's mercy, the inferior class of those to whom it is said, "Defraud not one another, except it be with consent for a time, that you may give yourselves to prayer; and come together again, that Satan tempt you not for your incontinency.
But I speak this by permission, and not of commandment." To such the same apostle also says, "Now therefore there is utterly a fault among you, that you go to law one with another;" while, in consideration of their infirmity, he adds, "If you have judgments of things pertaining to this life, set them to judge who are least esteemed in the Church." For in the kingdom of heaven there are not only those who, that they may be perfect, sell or leave all they have and follow the Lord; but others in the partnership of charity are joined like a mercenary force to the Christian army, to whom it will be said at last, "I was hungry, and you gave me meat," and so on.
Otherwise, there would be no salvation for those to whom the apostle gives so many anxious and particular directions about their families, telling the wives to be obedient to their husbands, and husbands to love their wives; children to obey their parents, and parents to bring up their children in the instruction and admonition of the Lord; servants to obey with fear their masters according to the flesh, and masters to render to their servants what is just and equal. The apostle is far from condemning such people as regardless of gospel precepts, or unworthy of eternal life.
For where the Lord exhorts the strong to attain perfection, saying, "If any man take not up his cross and follow me, he cannot be my disciple," He immediately adds, for the consolation of the weak, "Whoso receives a just man in the name of a just man shall receive a just man's reward; and whoso receives a prophet in the name of a prophet, shall receive a prophet's reward." So that not only he who gives Timothy a little wine for his stomach's sake, and his frequent infirmities, but he who gives to a strong man a cup of cold water only in the name of a disciple, shall not lose his reward.
Source: Reply to Faustus the Manichaean (New Advent)