something that is absolutely true or of great importance
—He always takes what his father says as gospel and never doubts anything he says.

Gospel means “good news,” and it’s the name given to the first four books of the New Testament, as they tell the story of Jesus. Gospel’s later meaning of “truth” came about because Christians believe that the Gospels are true. The Apostle Paul believed in the message of Jesus and gave his life to spreading that message:

For I am not ashamed of the gospel, for it is God’s power for salvation to everyone who believes, to the Jew first and also to the Greek. For the righteousness of God is revealed in the gospel from faith to faith, just as it is written, “The righteous by faith will live.” (Romans 1:16,17)

The Gospels of the Bible are known by the names of their authors, and are sometimes called “The Gospel According to Matthew,” “The Gospel According to Mark,” “The Gospel According to Luke,” and “The Gospel According to John.” When talking about someone’s version of the truth, or his views on life or a particular topic, people sometimes call that “the gospel according to” that person.