The emphasis here is on John’s words, “Live deeply in what you were taught.” What the Holy Spirit has taught you, insofar as the plans that God has for you, is unique to you.
This is an intensely personal thing. What we have learned from the word of the Spirit, through the intermediacy of human teachers, is to be the ground of our action. But our activity must always be based on the conviction of what has come home to us. In other words, we walk by faith in the Word of God as God has taught it to us and not by what we have learned by tradition. Tradition has, historically, been a deadly foe of the Church and has held people back from advancement in their spiritual life.
That means that we do not need to have a scholar interpreting the Word of God for us. We can be grateful for scholars, we can read their helpful comments, and the Lord will use them to teach us something, but we are not dependent on them. The Holy Spirit will instruct us.
We must be open, of course, to hear all that others have to say. Charles Spurgeon said, “I do not understand those men who have such a high opinion of what the Holy Spirit says to them, and such a low opinion of what He says to anyone else.” We must remember that the Spirit of God does speak through other people, as well as through us. But we must act only on what the Lord has said to us.
This obedience is where fruitfulness comes from. We can’t go another’s route, we can’t live another’s spiritual life for them, or force them to go our route. We must open the Word, pour over it, listen to the Holy Spirit in it, listen to others as the Holy Spirit has taught them, and then—faced with this array of external testimony—obey what the Spirit confirms to us as truth.