Let no man be offended that I here give a warning of this evil. That this sin is a quicksand that has sucked in, and destroyed thousands, is truly apparent both from Scripture and experience. Solomon tells us that it is a deep ditch, into which such as are abhorred of the Lord shall fall (Proverbs 22:14). O the multitudes of dead are there! And if so, I cannot in duty to God, or in love to you, be silent, where the danger is so great….The more ordinary and common sins of this kind are known by the names of adultery and fornication. The latter is when single persons come together out of the state of marriage. The former is, when at least one of the persons committing uncleanness is contracted in marriage. This is now the evil I shall warn you of. And, that you may never fall into this pit, I shall endeavour to hedge and fence up the way to it by these ensuing arguments. And O that the light of every argument may be powerfully reflected upon your conscience! Many men are wise in the generals, but very vain in the reasonings or imaginations, as the apostle calls them (Romans 1:21), i.e., in their practical inferences. They are good at speculation, but bunglers at application: but it is truth in the particulars, that, like a hot iron, pierces, and, O that you may find these to be such in your soul!
(Works of John Flavel, Vol 5)