Paul expounds on the vanity of the apostles’ preaching (1 Corinthians 15:14), should there be no resurrection from the dead. The implication would be that the apostles, whose testimony is centred on the resurrection of Christ, are false witnesses who tell lies about God. The words we testified about God
can also be translated as we testified against God.
Paul’s language comes from the legal sphere, where a witness swears an oath.
The Corinthians cannot claim to follow the apostles if they deny the centrepiece of the apostles’ message. If they hold the resurrection to be false, then they should reject the apostles as false prophets (see Deuteronomy 18:20–22).
Paul again states the implication that he has stated in the beginning (1 Corinthians 15:13). If there is no resurrection, then Christ has not been raised.
15 We are even found to be misrepresenting God, because we testified about God that he raised Christ, whom he did not raise if it is true that the dead are not raised.