2 Corinthians 3:6
2 Corinthians 3:66And He has qualified us as ministers of a new covenant, not of the letter but of the Spirit; for the letter kills, but the Spirit gives life.
The Watchtower restricts the new covenant to "spiritual Israel" — the 144,000 anointed. On this reading, ("he has made us adequately qualified to be ministers of a new covenant, not of a written code, but of spirit") applies only to the anointed class. The great crowd of other sheep are not parties to the new covenant but merely "benefit" from it — alien residents blessed by their association with the anointed, but not themselves sealed by its promises.
Put Paul's words alongside Jeremiah's prophecy they echo. The new covenant promise in says "they will all know me, from the least of them to the greatest of them," and its stated purpose is "I will forgive their error, and their sin I will remember no more." If you are excluded from the covenant, you are excluded from the forgiveness the covenant provides. Every human needs that forgiveness, and Paul applies "ministers of a new covenant" to "us" — the plain referent of Paul's letter to the Corinthian church, not a limited anointed subset.
The question to ask gently: " says Paul and his companions are ministers of the new covenant. says the covenant includes everyone 'from the least to the greatest.' has Jesus saying 'drink from it, all of you — this means my blood of the covenant, poured out for the forgiveness of sins.' If the forgiveness-of-sins covenant is only for 144,000, where is the great crowd's forgiveness? A covenant you are outside of is not better news than the old covenant — it is worse news."