But, on the other hand, those who are not bound by wedlock are to be admonished that they observe heavenly precepts all the more closely in that no yoke of carnal union bows them down to worldly cares; that, as they are free from the lawful burden of wedlock, the unlawful weight of earthly anxiety by no means press them down; that the last day find them all the more prepared, as it finds them less encumbered; lest from being free and able, and yet neglecting, to do better things, they therefore be found deserving of worse punishment.
Let them hear how the Apostle, when he would train certain persons for the grace of celibacy, did not contemn wedlock, but guarded against the worldly cares that are born of wedlock, saying, This I say for your profit, not that I may cast a snare upon you, but for that which is comely, and that you may attend upon the Lord without hindrance. For from wedlock proceed earthly anxieties; and therefore the teacher of the Gentiles persuaded his bearers to better things, lest they should be bound by earthly anxiety.
The man, then, whom, being single, the hindrance of secular cares impedes, though he has not subjected himself to wedlock, has still not escaped the burdens of wedlock. The single are to be admonished not to think that they can have intercourse with disengaged women without incurring the judgment of condemnation. For, when Paul inserted the vice of fornication among so many execrable crimes, he indicated the guilt of it, saying, Neither fornicators, nor idolaters, nor adulterers, nor effeminate, nor abusers of themselves with mankind, nor thieves, nor covetous, nor drunkards, nor revilers, nor extortioners, shall possess the kingdom of God .
And again, But fornicators and adulterers God will judge. They are therefore to be admonished that, if they suffer from the storms of temptation with risk to their safety, they should seek the port of wedlock. For it is written, It is better to marry than to burn. They come, in fact, to marriage without blame, if only they have not vowed better things. For whosoever has proposed to himself the attainment of a greater good has made unlawful the less good which before was lawful. For it is written, No man, having put his hand to the plough, and looking back, is fit for the kingdom of God . He therefore who has been intent on a more resolute purpose is convicted of looking back, if, leaving the larger good, he reverts to the least.
Source: Pastoral Rule (New Advent)