“Do not be deceived: ‘Bad company corrupts good morals,’” 1 Corinthians 15:33.
Paul was dealing with false teaching when he wrote this, the teaching of those who said that the dead are not raised. What then would be the deception? The belief that in taking up with those who teach falsely, our faith will not become corrupted in the process. This is the problem that the Corinthians faced; they had entertained the teaching of some, contrary to Scripture, that the dead are not raised, and the error had gained acceptance among some of the congregation. In the midst of his defense of the truth, Paul gives them this warning, that bad company corrupts. It is because they had not corrected the false teaching, but rather had let it abide, that the belief of some had become corrupted by it.
(Good morals here is to be understood as standing in the truth, standing in the doctrine of Christ. If we depart from this into false teaching, we have become immoral.)
It is an easy thing for a man to believe he is strong enough that he won’t be carried away with false doctrine if he consorts with those who teach it. How many men have thought, “I know they’re teaching error, but I will be a good example to them of the truth; they will become convinced.” But here, the message could not be clearer; we are plainly told that we deceive ourselves if we believe our faith will not be corrupted. Is this not why Jesus tells us, “Watch out and beware of the leaven of the Pharisees and Sadducees”? Was not Barnabas carried away into the error of the circumcision party, Galatians 2:13, and Solomon corrupted by his wives, 1 Kings 11:4, Nehemiah 13:25-26?
He warns them as well to be sober-minded. They had become carried away by a fancy; carried away into non-doctrinal teaching. As the drunk man loses control of his normal mental processes, but is carried into an alternate reality, which has no connection to the true and correct perception of life, so the man who has been carried off into error is not sober in his relation to God, but has wandered off into teachings which lead him astray, away from the true and correct truth of the gospel, for, “The sum of Your word is truth, And every one of Your righteous ordinances is everlasting,” Psalm 119:160, and again, “Sanctify them in the truth; Your word is truth,” John 17:17.