4 What troubles matrimony involves you have learned in the marriage state itself; you have been surfeited with quails' flesh even to loathing; your mouth has been filled with the gall of bitterness; you have expelled the indigestible and unwholesome food; you have relieved a heaving stomach. Why will you again swallow what has disagreed with you? “The dog is turned to his own vomit again and the sow that was washed to her wallowing in the mire.” Even brute beasts and flying birds do not fall into the same snares twice.
Do you fear extinction for the line of Camillus if you do not present your father with some little fellow to crawl upon his breast and slobber his neck? As if all who marry have children! And as if when they do come, they always resemble their forefathers! Did Cicero's son exhibit his father's eloquence? Had your own Cornelia, pattern at once of chastity and of fruitfulness, cause to rejoice that she was mother of her Gracchi? It is ridiculous to expect as certain the offspring which many, as you can see, have not got, while others who have had it have lost it again.
To whom then are you to leave your great riches? To Christ who cannot die. Whom shall you make your heir? The same who is already your Lord. Your father will be sorry but Christ will be glad; your family will grieve but the angels will rejoice with you. Let your father do what he likes with what is his own. You are not his to whom you have been born, but His to whom you have been born again, and who has purchased you at a great price with His own blood.
Source: Letters (New Advent)