How do we know the Gospel of John is true?

In John 14:26, Jesus promises that the Holy Spirit will teach us all things and remind us of His teachings. This divine assistance ensures that the truths recorded in the Gospel of John are accurate and trustworthy. Additionally, the consistency and fulfillment of Old Testament prophecies in the life and works of Jesus affirm the credibility of John's account. Believers can thus have confidence in the truth of the Gospel through the Spirit's confirmation in their hearts and the corroborative evidence found in Scripture.