The people at Corinth had already been told these things, and they had ignored them. That is a sad thing, when we go on in the Christian life and we think we can pick and choose the things we pay attention to, and not worry so much about various things that don’t appeal to us.
Interestingly, there is a lost letter, so called, to the Corinthians, referred to in 1 Corinthians 5.9. This is the famous lost letter which the apostle, almost in a throwaway remark, refers to: ‘I wrote to you in an epistle not to company with fornicators.’ ‘Where is that letter?’ it is asked. ‘Oh, if we could find it, how interesting, you would be adding to the Bible, wouldn’t you?’ Can you add to the Bible? Of course not! We know there is a lost letter but it quite clearly was not part of the inspired body of books of the Bible. Paul with a pastoral heart had written them a letter. We do not know how long – may be only a few lines – and it would have been true, I am sure, and it would have been correct teaching, but it did not happen to be one of his inspired letters; especially inspired by the Spirit of God, to be preserved for all time. If it had been, then you may be sure that it would have been preserved by the power of God, because God does preserve his word and we have it intact and perfect. God did not intend it to be in the Scripture. Not because it was in error; not because there was any fault in it, but because, as he has designed the Scripture to be perfect and complete without it. The category of inspired prophecy is larger than what has been preserved in Scripture. We read of true prophets who have contributed not a single word to Scripture (1 Samuel 10:5; 1 Kings 18:4; 1 Corinthians 14:29). So, if somebody finds the pre-first letter to the Corinthians somewhere in a pot in some ancient cave, here is what we have to say about it. Possibility (1) it is a forgery – there are a lot of forgeries about – or, alternatively (2), it is a most interesting letter but it doesn’t actually belong in the Scripture because if it did, it would be already there. We call this 1 Corinthians, though according to the apostle it is, strictly speaking 2 Corinthians, but this is the first of the inspired letters to Corinth by the apostle Paul.