Mark 16:17
Mark 16:1717And these signs will accompany those who believe: In My name they will drive out demons; they will speak in new tongues;
The Watchtower treats as textually disputed and brackets it accordingly in the NWT — and along with it. JW publications use the textual question to dismiss any charismatic or continuationist reading of the verse, then pivot to Acts 8 / Acts 19 to argue tongues ceased with apostolic laying-on-of-hands. The cessation argument is structured to avoid having do any apologetic work at all.
Protestants are divided on (the longer ending) on textual grounds, and that intramural debate is not relevant to the JW conversation. What matters is that the Watchtower's wider cessationist case rests on a self-contradicting structure: the rs book rejects the standard cessationist reading of (treating "the perfect" as still future) yet stakes cessation on a mechanism (apostolic laying-on-of-hands) that falsifies — the Spirit fell on the Gentiles at Cornelius's house before any apostolic prayer or laying on of hands. is a side-issue. The decisive text is Acts 10 in the Witness's own NWT, where Peter himself reports what happened.
The NWT brackets as textually disputed and renders v. 17 as "By the use of my name they will expel demons, they will speak with tongues" — inserting "by the use of" (where the Greek has simply en tō onomati mou, "in my name") and dropping "new" from "new tongues" (kainais glōssais). The dropping of "new" is a small change that nudges away from the apostolic-era glossolalia category and toward a more generic "tongues" reference. The bracketing serves the cessationist apologetic in the rs book — the longer ending is treated as non-canonical whenever it would otherwise authorise sign gifts in the post-apostolic church.