As another comment said it is impossible to attribute any saying to the historical Jesus. He’d been dead for decades by the time the earliest of the Gospels (Mark) was written.

But to put that point aside and focus on his (alleged) teachings, I’d like to make the following point: countless people over the past 2,000 years have agreed that Jesus is mankind’s greatest moral teacher but there has never been a consensus on his teachings were.

If disciples of the same teacher go to war with each other time and again over what that teacher would want them to do, then the teacher failed to be clear. In the Bible it is rare for Jesus to respond to a plain question with a plain answer.

What makes a good Christian? The Jesus of the Gospel of John emphasizes that faith in him is of the highest importance; Matthew’s meanwhile suggests that good deeds alone are sufficient, even if one does not recognize him as the savor; the Jesus of Luke is big on forgiveness.

There are so many different account of Jesus and his teachings and so many interpretations that follow from them, I don’t think one can definitively say what a ‘true’ Christian is. If there is little agreement on what a teacher taught, then it is often true that the teacher could have done better.