What does John 20:31 mean?

John's gospel was written long after the accounts of Matthew, Mark, and Luke. Since those writings were established, and their details known, John's writing diverges to show a different perspective. His choice of which details to include, and which to omit, is not an accident. Every writer has some purpose in mind, and John's purpose is stated here. He wants those who read these words to understand that Jesus is the Savior and the Son of God (John 20:30).

John has not included every single detail, nor could he (John 21:25). Even if he could, it wouldn't matter to those who refuse to accept belief (John 5:29–30). Rather, this book chooses certain points to complement those found in the other writings. When John writes his letters, now known as 1 John, 2 John, and 3 John, and his Revelation, the same theme will apply. The purpose of Scripture is to reveal these crucial truths (2 Timothy 3:16) so disciples can have an objective source of godly wisdom (1 Corinthians 4:6).