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The “all truth” they would receive was not the truth about every bit of knowledge in the universe, from supernovas to DNA. The “truth” refers to the whole truth about everything bound up in Jesus Christ, the way, the truth, and the life. The Spirit will illuminate the things that are to come (John 16:13), not in a predictive sense, but in so far as he will unpack the significance of the events yet to come, namely Jesus’ death, resurrection, and exaltation. The Spirit, speaking for the Father and the Son, will help the apostles remember what Jesus said and understand the true meaning of who Jesus is and what he accomplished (John 14:26).
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