It is a common misunderstanding that the verse you quoted applies to every believer. The context was that the promise was given to the apostles who then had all truth revealled to them which they wrote down...aka the Scriptures. Calvin notes, "The Spirit, whom Christ promised to the apostles, is declared to be perfect Master or Teacher of truth And why was he promised, but that they might deliver from hand to hand the wisdom which they had received from him? The Spirit was given to them, and under his guidance and direction they discharged the office to which they had been appointed. He will lead you into all truth. That very Spirit had lead them into all truth, when they committed to writing the substance of their doctrine. Whoever imagines that anything must be added to their doctrine, as if it were imperfect and but half-finished, not only accuses the apostles of dishonesty, but blasphemes against the Spirit If the doctrine which they committed to writing had proceeded from mere learners or persons imperfectly taught, an addition to it would not have been superfluous; but now that their writings may be regarded as perpetual records of that revelation which was promised and given to them, nothing can be added to them without doing grievous injury to the Holy Spirit."