Every word of Jesus is true and vital, but not every word was spoken to you. Much of what He said was addressed to people still under the law, before the cross. Read the red letters through the finished work, not above it.
The Grace Answer
A lot of sincere believers treat the red letters as a higher tier of Scripture, as if the words Jesus spoke outrank the rest and can be lifted straight off the page and applied without context. It sounds reverent. It actually creates confusion, because Jesus said things like sell everything, cut off your hand, and forgive or you will not be forgiven, right alongside the tenderest grace in the Bible.
The missing piece is timing. The Gospels are a hinge. Jesus lived, taught, and died under the old covenant, because the new covenant does not begin until His death. “For where there is a testament, there must also of necessity be the death of the testator.” A will takes effect when the one who made it dies. So during His earthly ministry, Jesus is often holding people to the law He came to fulfill, exposing the self-righteous, and quietly leaking the grace that is about to break loose.
How to read them well
This does not shrink Jesus' words. It lets them land correctly. Ask of any red-letter passage: who is He talking to, and where are we in the story? Is He raising the law to expose a need, confronting religious pride, or previewing the grace of the cross? Read that way, the hard sayings stop contradicting the gospel and start pointing to it.
And nothing about this pits Jesus against Paul. Paul is not overruling Christ. Paul is unpacking what Christ accomplished, explaining the covenant Jesus' death put into effect. So keep the red letters precious. Just read them through the cross rather than as if the cross had not happened yet, and they open up instead of tangling. The words in red are not a fifth gospel with higher authority. They are the voice of the One the whole Bible is about, and they shine brightest when the cross is the light you read them by.