When we first read the Bible we don't believe that anybody would put words into the mouth of Jesus.
The more we study the gospels the more evident it becomes that this is exactly what the writers of the Gospels have done.
One example is early in the Gospel of Matthew:
"'and whoever does not take up the cross and follow me is not worthy of me.'" Matthew 10:38 (NRSV)
Think about this for a moment.
How could Jesus have referred to taking up the cross in this way when he had not been crucified yet?
The expression taking up the cross refers to Jesus' self-sacrifice, and that expression could not have been in use before Jesus' crucifixion.
Jesus would not have spoken in this way so early in his ministry.
It is impossible.
So the Gospel writers, who were writing decades after Jesus' death on the cross, have put these words into Jesus' mouth to make a philosophical point - that you must suffer and sacrifice yourself for others.
But Jesus himself could never have said these words.
[Scripture quotations (marked NRSV) are taken from the New Revised Standard Version Bible, copyright 1989 by the Division of Christian Education of the National Council of the Churches of Christ in the U.S.A., and are used by permission. All rights reserved.]