This is a common theory, that Jesus said things that Paul later contradicted.
But Paul was more or less another of the followers of Jesus. There were times when he seemed more on target than even Peter. Paul witnessed the stoning of Thomas, and it seems to have made an impression on him. He was trying to destroy Christianity, and after Dasmascus it was preserved as vibrant as ever. The early Christians were a devoted people, willing to die for his faith like the others. Paul was committed to the Christian faith, and willing to pay the cost.
What I do dispute is that Constantine was a follower of Jesus. Oh sure, you hear this story about the dream with the shields and chi ro on them. That's nice and all, but from what I see, Constantine helped get rid of the vibrant Early Church which traveled the land and was willing to die for their faith, in favor of the Catholic church, a collection of pompous rituals and incense, fancy robes, rigid hierarchy, and a number of heresies.
Luther was a follower of Jesus. He helped dredge the real Christianity out of this mire. But Constantine? Nah, he almost destroyed the Church.
Now back to the apparent contradiction to what Jesus said in Paul's words. For one, Paul was a mere human, with a flawed grasp on Jesus, so some of this can be excused. But also, most people deeply misunderstand Jesus. Case in point, they often try to place him as a socialist.
But neither was he a gun-toting capitalist. And many of them try to paint him as a gentle and meek type, who supported taxes. Oh did he? He once suggested people get their tax money out of a fish. But surely he said "render unto Caesar", yeah you should read this.
Jesus meant that what is Caesar's according to Jewish thinking, is nothing. That we need to make a choice between the state and God.
So, back to Jesus's parables. We have a number of them that seem to be very harsh and seem to take a very dim view on sin, yet Paul talks a great deal on grace. The idea behind the Pauline heresy theory, I suppose, is that grace is some false teaching, and that those who don't follow Jesus's harshest teaching are liable to judgement. But I contend that you've missed the actual point of all of his "outer darkness" parables. First, consider who he is speaking to. That's a big hint. To sinners, he offered a great deal of grace, when the world mostly turned its back on them (but here also is Jesus misunderstood as someone telling people to forgive everyone. Sin itself is forgiven, but the neighbor in the Good Samaritan is not the one who acts with malice, and robs and beats up the guy, nor any who are aloof and give social distance to the man, but the one who has MERCY). But to the Pharisees he told a great number of parables of judgement. Why? Because they had no mercy.
Jesus's parables come in two main flavors:
- "The kingdom of heaven/God is like" parables
- "I didn't say Simon says" parables, where a "master"is mentioned, but a closer reading determines the master is not actually God, but the Pharisees perception of God, as an unjust and unforgiving lawmaker. I call these "I didn't say Simon says" because they seem to be about God, but he doesn't say "the kingdom of heaven/God is like..."
For those who have mercy, Jesus has mercy, even to a repentant thief dying on the cross with Jesus. To those more concerned with self-justifying their lack of forgiveness, would they want God to treat them as they deserve?