How it is that, just as a great reward is due to the monk who labours according to the regulations of the fathers, so likewise punishment must he inflicted on an idle one; and therefore no one should be admitted into a monastery too easily.
For as unbounded glory hereafter is promised to those who faithfully serve God and cleave to Him according to the rule of this system; so the severest penalties are in store for those who have carried it out carelessly and coldly, and have failed to show to Him fruits of holiness corresponding to what they professed or what they were believed by men to be. For “it is better,” as Scripture says, “that a man should not vow rather than that he should vow and not pay;” and “Cursed is he that does the work of the Lord carelessly.” Therefore you were for a long while declined by us, not as if we did not desire with all our hearts to secure your salvation and the salvation of all, nor as if we did not care to go to meet even afar off those who are longing to be converted to Christ; but for fear lest if we received you rashly we might make ourselves guilty in the sight of God of levity, and make you incur a yet heavier punishment, if, when you had been too easily admitted by us without realizing the responsibility of this profession, you had afterwards turned out a deserter or lukewarm. Wherefore you ought in the first instance to learn the actual reason for the renunciation of the world, and when you have seen this, you can be taught more plainly what you ought to do, from the reason for it.
Source: Institutes (New Advent)