A professor I had said that for centuries Christians have substituted the ideas of Paul for the true teachings of Jesus. What do you say about this?

Paul said that he was commissioned by Jesus to preach the gospel (see 1 Cor. 1:17) and the gospel message predates Paul, so it could not have originated with him. The gospel message is presented throughout the Bible, from the prophecies of the One to come, to Paul’s writings about the life, death, burial, and resurrection of Jesus.

Paul’s writings, specifically 1 Corinthians 15:3-5, echoes a creedal statement that scholars date to within mere months after the crucifixion (see The Case for the Resurrection, by Gary R. Habermas and Michael Licona). This creedal statement is an affirmation of what really took place, which Jesus Himself spoke about (Mark 10:32-34; Matt. 20:17-19) and which Peter proclaimed on the Day of Pentecost (see Acts 2).

Christians do not “substitute the ideas of Paul for the teachings of Jesus.” “The ideas” (the teachings) of Paul affirm and illuminate what Jesus taught in His earthly ministry. Paul’s teachings also include further revelation, given to him by Jesus, to edify and grow the Church. So when Christians preach and teach Paul’s words, they are faithfully sharing God’s words.