What do we do with those red letters in the Bible? Did Jesus really say those words? Or did the church just make up sayings related to the issue of the day and place them in the mouth of Jesus? New Testament scholar Birger Gerhardsson puts this question into perspective by looking at the example of Paul.
“Finally, we observe how Paul proceeds when he does not have a specific word from Jesus to support him. He then states without circumlocution that in such cases he cannot refer to any command of the Lord, but is simply providing his own opinion. Theses passages are embarrassing evidence against the common opinion that in the early church no distinction was made between what was said ‘by the Lord [himself]‘ and what was said by some one else ‘in the Lord'; that words were freely constructed, or that sayings of some early Christian prophet were freely placed in the mouth of Jesus. In 1 Corinthians 7 we see how such a man as Paul, at least on one occasion very clearly upheld the distinction between that which was said ‘by the Lord’ and that which was said ‘in the Lord.'” (Reliability of the Gospel Tradition, p. 20)