The Gospel changed the world. That teaching came with many proofs: God's character, internal consistency, prophecies (esp messianic), miracles of its authors, miracles of its followers, life transformations, and global impact. That same message, that Jesus Christ our God died in our place, has accomplished all this for hundreds of millions of people in almost 200 countries. People from all walks of life, many denominations, etc have vetted those manuscripts, too.
Almost 2,000 years later, new groups showed up who say we can't trust any of that. Their come with contradictory teachings, their own Bible translations, and usually one or more organizations that must be believed and obeyed at all costs. Those organizations claim to have the real truth. One is Watchtower, aka Jehovah's Witnesses.
God's Word says to test everything and everyone like the Bereans did. The reason is that humans fail with many lying. Jesus warned piles of false prophets would come. Most would deny or take the focus off of Him. They would bring in alternative gospels. We must test everything.
Jesus quoted the Word of God (i.e. Old Testament) saying it had full authority. That means Jesus trusted His copy of God's Word, likely the Septuagint. That shows that God makes sure His Word makes it to His people. If God can't protect His Word, and His Word is life, then God has failed. We'd have to toss out the whole Bible. Since God can't fail, you can trust His Spirit provided good translations to check new claims. It started being passed down orally, then on manuscripts, and then translated. Some translations, like KJV and ESV (mine), have been checked by hundreds of language experts for decades to centuries. Both Watchtower's claims and NWT translation should be checked against existing, vetted Bibles to spot corruptions.
Look at the Bereans again. Notice that they didn't just blindly believe Paul's teaching. They diligently checked every doctrine he said against their Scriptures. That's good because God's prophets and apostles had plenty of failures. Also, Paul had to counter Peter when he got into false teaching. In contrast, most Jehovah's Witnesses trust everything Watchtower says by default, trust NWT with no cross-checking, and (unlike Jesus and Bereans) reject all prior translations. That is sin because God's Word says Watchtower isn't God: they're just people who can fail like everyone else.
We're commanded to test the people, too. They must live in a Christ-like way. Christ Himself had no sin. The Apostles were blameless. In ministry, they were very humble. They also worked miracles to prove they had God's authority. Their doctrines never contradicted Scripture. To compare, we'll do a brief history of the JW organization (their character) followed by a test of their doctrines.
Note: For Bible passages, I'll link to verses on sites that have every major translation on them. Cross-check them yourselves!
In the 1800's, a group of Adventists who falsely predicted the return of Christ splintered into new groups. Charles Taze Russell formed Zion's Watchtower Tract Society to push his newer beliefs. Russell's doctrines contradicted both Scripture and all work of the Holy Spirit in the global church up to that point. Unlike the early church, Russell worked no miracles to prove God was behind his claims. Yet, he claimed all those Christians on my evidence page were liars (or deluded). A person acting like this is a warning sign that they're motivated by ego or money. What kind of person was Russell?
Unlike Jesus and the Apostles, Russell wasn't blameless before others of his time. His wife divorced him claiming he was an egomaniac, abusive, a cheater, and lived grand off followers' money. One critic said he had no credentials or knowledge of Greek. When, Russel sued him for defamation, most reports say Russel admitted under cross-examination that he didn't know Greek at all. Not even the alphabet. So far, Russell has less character and Biblical scholar than the teachers that came before him.
Later, with a new leader (Rutherford) and re-branding, they called themselves "Jehovah's Witnesses" who read "The Watchtower." Many followers left because they didn't accept the new practices and theology. ISBA, which JW.org says Russell founded, still exists. Their about page lists Russell's doctrines, claim ISBA are the true heirs, and that Rutherford's Jehovah's Witnesses are a disobedient offshoot. How can we trust JW's if most of the early followers left saying the JW group was fake? Do we follow Rutherford's JW's (Watchtower) or their original teachings (ISBA) or trust neither?
What Bible Russell use to derive their teachings? Russell and ISBA used the Emphatic Diaglott made by a Greek scholar. ISBA/Watchtower bought the copyright to this Bible for their own uses. Archive.org has a scanned copy whose copyright lists "IBSA" and "Watchtower" as owning and distributing Emphatic Diaglott. Amazon still sells it with ISBA's as the publisher. This was the original Bible endorsed by Watchtower.
Why use Wilson's translation? Russel liked that it added "Jehovah" to the NT in places where it wasn't there. It would say "Lord" in the Greek but they'd put Jehovah. On slide 296, we see John 1:1 says Jesus "was God." In John 8:58, it also has Jesus saying "Before Abraham was, I am" with same present tense as every major translation. That means the very Bible that Watchtower used for their studies plainly said Jesus is God, contradicting their beliefs. What to do?
If the Bible disagrees with our beliefs, we change our beliefs to fit the Bible. Instead, they changed the wording of specific passages to fit their beliefs. John 1:1 changed from "was God" to "was a god." John 8:58 from "I am" to "I have been" even though there's no past tense in Greek version. After enough changes, this "New World Translation" became their new "bible." It should arouse suspicion in readers that every expert in Biblical languages... Christian, Catholic, language historians... all went in a different direction than Watchtower's translators. Even Watchtower's first Bible disagreed with their new one! That's how you know they're either incompetent translators... or liars.
Enough history. Let's look at something more trustworthy: God's Word. We'll compare Russell's and his successors' beliefs to the Word of God. We'll also consider the teachings that the Holy Spirit gave the church for the past 2,000 years.
For each doctrine, we'll do Watchtower's claim followed by the Bible's. We'll use links either directly to Bible verses or sites with lots of them. Let's go!
Claim: All prior Christian doctrines were often a result of the evils of Constantine and the King James Bible.
Counter: We'll address Constantine later. For Bibles, we read all kinds of translations that all go back to the Hebrew, Aramaic, and Greek with wide, peer review. Theirs came much later and contradicts the others. Which is more suspicious? If KJV and all other Bibles could be corrupted, shouldn't Watchtower readers likewise test the New World Translation and Watchtower's materials for errors or corruption?
I'll default on ESV on a site, BibleGateway, that lets you check the passage in any translation. Alternatively, you can see many at once for a single verse on BibleHub. Example: John 1:1. One translation diverging from all the others, esp basic Greek, is a sign they're getting it wrong or maliciously copied others.
Claim: There is no Hell. God wouldn't have wrath like that. This was one of Russell's first beliefs.
Counter: Jesus mentioned Hell more than anyone else. He describes it as a punishment by an angry master. He describes it as an agonizing place. He specifically says to fear He who can put you in Hell more than destruction of your body. In Revelation 14:9-11, God's wrath is poured out on those who take the mark of the beast. They are tormented in fire "forever and ever." What Scripture plainly teaches, like in Exodus 34:6-7, is that God is by nature as just and wrathful as He is loving and forgiving.
Claim: Christ returned as a spirit, not a body.
Counter: It's not clear how they'd ever think this just reading Scripture. In Luke 24:36-43, they think Jesus is a ghost (or spirit). Jesus says He is not a ghost, that He has flesh, and showed His pierced hands and feet. Then, He ate with them. In John 20:26-29, Thomas also touched his wounds. He's definitely physical.
Claim: Christ did not always exist. These claims were fabricated by or after Constantine in 300+AD.
Counter: The Messianic prophecies, esp Micah 5:2 and Isaiah 9:6, say the Messiah will be God and is "everlasting." In 1 Tim. 1:15-17, Paul is talking about Jesus. He calls Jesus "eternal," "immortal," "invisible," and "the only God." Even the earliest church fathers believed Jesus Christ always existed and is God. Ignatius (eg 100AD) even quotes John 1:1 saying the Word "was God." They knew Jesus Christ was God.
Claim: Christ is not God.
Counter: He claimed to be in ways his audience understood clearly. He especially did it in John 8:58 by replying "I am," God's name. Although it's present tense in the Greek, NWT changes it to past tense in the English to mislead readers. (Dangerous.) Jesus also worked miracles by speaking on His own authority, not only praying. Like God did for Moses, Christ gave the 12 (Matt. 10) and the 72 (Luke 10) authority to work miracles and cast out demons. Only God (Isa. 43:25; Jer. 31:31-34) and Christ (Mark 2:1-12) forgive sins. He often commands it or says "I" like He is God. Only God receives worship and so did Christ: Matt. 28:5-9, Matt. 28:16-17, Luke 24:50-53, John 9:35-38, and John 20:27-28.
Claim: Jesus is Michael the Archangel.
Counter: Scripture never says Jesus is Michael. Watchtower just made this up. Hebrews 1 argues Christ is different than and above all the angels.
Claim: Holy Spirit is a force, not a person.
Counter: This article has a pile of Bible passages showing the Spirit speaks, prays, comforts, is grieved, and so on. Only a person can do these things: inanimate objects, like electricity or wind, can't speak or feel grief. For speaking examples, read Acts 8:29 and Rev. 14:13 for actual words, and speaking examples in Acts 11:12 and 1 Pet. 1:11. The Holy Spirit is both speaking to people and responding in Rev. 14:13 to what they say. He's conversing.
Claim: Trinity isn't true.
Counter: Far as the Trinity, the Bible teaches that the Father, the Son, and the Holy Spirit are separate persons in some way. It also teaches they're the one, true God. It does this in a series of passages that are never integrated into one, clear teaching. God does that for a lot of topics, maybe to make us dig into His Word. Later, Christians put together the Trinity: a theology based on those verses (examples) that spells out what they say. We don't claim to understand it, though. We just believe His Word.
Claim: Jesus returned invisibly in 1914.
Counter: They obviously can't prove this from the Bible. In God's Word, Jesus says nobody will know the day or time, people will lie about it, and the real thing will be visible to everyone. See Matt. 24:23-36 for many, esp v23 and v36. In 1 Thes. 4:13-5:3, Paul says it will happen unpredictably with an archangel shouting and trumpets of God. Again, it's an unpredictable event that nobody will miss when it happens.
(Read the Gospel, see proof it's true, or learn to live it.)