Galatians 2:5
Galatians 2:55We did not give in to them for a moment, so that the truth of the gospel would remain with you.
Read as Paul standing firm against those who would corrupt Christian teaching, which the Watchtower applies to its own defence of doctrine against Christendom. The phrase "the truth of the good news" is heard through the organisation's own use of "the Truth" as a name for its body of teaching and for membership in it.
This is a vocabulary check rather than an argument, and it works best as a gentle question. Look at what "the truth" is attached to in this verse: the good news. Not a body of doctrine held by a group, and not the group itself — the gospel message. Paul refused to yield so that the truth of the gospel would remain with the Galatians. That is the consistent New Testament pattern. Jesus says "I am the truth" (). The Spirit is "the Spirit of truth" (). Paul speaks of "the word of the truth, the good news" (). John rejoices to find children "walking in the truth" (, ) — meaning living by the gospel. A person, the Spirit, and the message. Never an organisation. So when a Witness says they came into the Truth, or that someone left the Truth, ask — without any edge in it — whether they came to a person or to an organisation, and read a couple of these verses together. Most have never noticed that their own vocabulary has no biblical parallel. Compare , , .