Deuteronomy 18:20
Deuteronomy 18:2020But if any prophet dares to speak a message in My name that I have not commanded him to speak, or to speak in the name of other gods, that prophet must be put to death.”
JWs treat Deut 18:20 as an Old Testament rule about ancient Israelite prophets and insulate the Watchtower from it on two fronts. First, the organisation insists it has "never claimed to be inspired prophets — only imperfect men doing their best," so the death-penalty clause for "speaking presumptuously in my name" is said not to apply. Second, every failed prediction (1874, 1914, 1925, 1975, the literal-then-overlapping generation) is recategorised as "expectation," "human understanding," or "running ahead of Jehovah's chariot." is then deployed to dress doctrinal reversal as "light getting brighter," and members who pioneered or sold homes on Watchtower instructions are blamed for having "read too much into" what the organisation itself published.
Deut 18:20 forbids two distinct offences in a single verse: (1) speaking a word presumptuously in Jehovah's name that he did not command, and (2) speaking in the name of other gods. The Watchtower fails on both counts simultaneously — which is why this verse and Deut 13 are best deployed together. On count one: the 1922 Watchtower described its dates as carrying "the stamp of approval of Almighty God"; the October 15, 1966 Watchtower called its chronology "trustworthy Bible chronology"; the August 15, 1968 Watchtower asked "Why Are You Looking Forward to 1975?" and put the gap between Adam and the 6,000-year mark at "weeks or months, not years"; the 1972 Watchtower (April 1, p. 197) identified the organisation itself as a modern-day "prophet" commissioned by Jehovah; the May 1974 Kingdom Ministry commended brothers selling homes because of "the short time remaining." That is not "expectation" — it is the Watchtower voluntarily submitting itself to the test of Deut 18:20 by speaking in Jehovah's name. On count two: the Arian Jesus the Watchtower preaches (a created Michael, not the uncreated God of Col 1:16-17 and ) is a different Jesus and therefore a different God in the sense Deut 13:1-5 describes. Either failure is fatal under the verse; both together are decisive. The insulation language ("we never said inspired") does not survive contact with the published record — and even granting it for argument's sake, Deut 13 still stands.