John 15:26
John 15:2626When the Advocate comes, whom I will send to you from the Father—the Spirit of truth who proceeds from the Father—He will testify about Me.
The holy spirit is taught to be God's impersonal active force, so "the helper" is understood as that force in operation, and "bearing witness" as the effect it produces in believers. The phrase "the spirit of the truth" is read as the force that conveys accurate teaching — which, in Watchtower framing, arrives through the organisation.
Two observations, and the first is a vocabulary point that costs nothing to raise. Jesus calls the Spirit "the spirit of the truth," which is one of the New Testament's three referents for that phrase. The truth is Jesus himself (), the Spirit (here and at 16:13), and the gospel message (, ). Never an organisation. If a Witness uses "the Truth" as a name for the group, this is a gentle place to notice the difference. Second, look at what the helper does. He comes, he is sent, and he bears witness about Jesus. Testifying is something a person does — it requires knowing something and choosing to say it. Across this discourse the same one teaches (14:26), guides, hears and speaks (16:13), and receives from the Son and declares it (16:15). Jesus also calls him "another helper," using a word meaning another of the same kind as himself. A force does not bear witness. Ask a Witness what it would look like for electricity to testify about someone. Compare , , .