What does John 14:26 mean?
Modern readers can read through the entire New Testament, with the benefit of more than two thousand years of scholarship. That makes it easy to laugh at the disciples for being dense—some of their responses to Jesus' teachings seem downright stupid (Matthew 16:11; Luke 24:25). It's crucial to remember there was no way for these men to fully grasp everything He was teaching until after those things had been accomplished. They did not yet have the New Testament, and they hadn't yet seen everything that was to come.Their experiences were crucial, but they also needed the teaching influence of the Holy Spirit (1 Corinthians 2:14). Especially in the case of Jesus' closest followers, the Holy Spirit will be instrumental in connecting His prior comments to their intended message (John 2:18–22; 12:16; Luke 24:6–8).
This statement is often misinterpreted by tearing it away from its context. As part of this discourse, Jesus is speaking of the teachings He delivered while on earth. It's not a guarantee of expertise in all earthly topics. Nor is the indication the Spirit will "teach you all things," in any sense, a promise that the Holy Spirit will deliver new revelations, or ongoing revelations, or personal revelations. The consistent theme of this passage is that the Spirit's role is to reinforce that which Christ has already taught. Godly guidance through the Holy Spirit bolsters the truths of His Word (1 Corinthians 4:6–7).