I just got through reading parts (I confess, I didn't read the whole thing) of Reasoning from the Scriptures with the Jehovah's Witnesses by Ron Rhodes, a former faculty member of Dallas Theological Seminary. I didn't know a lot about Jehovah's Witnesses other than they like to do door-to-door evangelism, they have a publication arm called The Watchtower, and the places they meet in are called Kingdom Halls. This book mapped out some of the contours of their theology, practices, and history for me. I thought I'd share some brief takeaways.
Beliefs about Jesus
When it comes to Christian theology, one of the most important things you can talk about is Jesus.
While the Trinity is involved in salvation, and the three persons of the Trinity are equal, Jesus is the one around whom God's work of salvation centers; therefore he tends to get most of the emphasis and discussion. What you say and believe about Jesus carries particular freight theologically.
Jehovah's Witnesses believe that Jesus is not equal with God, and is a creature that God made who has some god-like qualities. They also reject the historic Christian teaching of the Trinity.
A central feature of Watchtower theology is that Jesus is not Jehovah. They say Jesus was a created angel–Michael the Archangel, to be more specific. The Watchtower magazine suggests, "There is Scriptural evidence for concluding that Michael was the name of Jesus Christ before he left heaven and after his return." Indeed, "Michael the great prince is none other than Jesus Christ himself" (p. 52).This actually is a variation of what came to be condemned in church history as a heresy: Arianism. It took the church a while to flesh out how best to understand God, Jesus, and the Holy Spirit, and there were debates about this in early church history in the first few centuries. Arius believed that Jesus was not co-eternal with the Father, but was created at a certain point in time. He and his followers made much of the subordinationist passages pertaining to Jesus in the Bible (as Jehovah's Witnesses also do), but didn't seem to sufficiently grapple with the claims to divinity and eternality of the Son (see, for instance, John 1 or 10:30, along with several other places). Rhodes' book takes a deep dive into the biblical evidence if you're curious.
Also, Jehovah's Witnesses deny the physical resurrection of Jesus.
When Jesus died, He became nonexistent and was raised (or, more accurately, was re-created) three days later as a spirit creature–that is, as Michael the Archangel. A physical resurrection did not occur. In Studies of the Scriptures, we find this statement: "We deny that He was raised in the flesh, and challenge any statement to that effect as being unscriptural" (p. 71).Rejecting a physical resurrection doesn't make good sense of several aspects of the different Gospels accounts, in which Jesus invites Thomas to touch his scarred hands and side (John 20:24-29), or when Jesus tells Mary Magdalene "Don't hold on to me" (John 20:17, implying that she had embraced or was holding him in some way). In Luke 24:37-43, Jesus invites the disciples to touch him and see his hands and feet, and he eats a piece of fish in front of them; he says in verse 39–"Touch me and see; a ghost does not have flesh and bones, as you see I have." Paul views the physical resurrection of Jesus as an essential belief to being a Christian in 1 Corinthians 15 (see especially verses 12-19, but the whole chapter is on resurrection). See also Romans 8:11, 23; 2 Corinthians 4:14 Philippians 3:20-21; it's also part of the Apostles' Creed. I like the way Richard Hays talks about it in his 1 Corinthians commentary: to deny a physical resurrection is to deny God's proclamation of goodness over creation in Genesis 1-2. God created human beings with bodies and said it was good. Yes, there is brokenness and sin in the created world, undeniably so. Some of that brokenness afflicts human bodies with frustrations and temptations, and sometimes we use our bodies to sin. But if you try to make God's answer to sin and brokenness be a total destruction of the earth and the body, you end up turning God's earlier pronouncement of goodness in Genesis into a lie. Why destroy something good along with the bad? Paul talks about a resurrection "body," and not just a spirit in 1 Corinthians 15, as well as the liberation of all creation from decay in Romans 8. Full, final salvation will involve the healing and glorification of our bodies as well as the healing and glorification of creation (though that healing comes through purifying fire of God's judgment, see 2 Peter 3). God preserves and perfects what is good (creation, bodily existence), while disposing of what is bad (sin, death, evil).
New World Translation
Jehovah's Witnesses have their own translation of the Bible called the New World Translation, and there are some funny things going on with it. Many Bible scholars who are aware of all the data and manuscript evidence criticize it as being outright inventive and irresponsible. Bruce Metzger, one of the most famous textual critics and Bible translators of a previous generation who worked at Princeton Theological Seminary, "calls the New World Translation 'a frightful mistranslation,' 'erroneous,' 'pernicious,' and 'reprehensible'" (p. 96). There are instances where words are poorly translated or outright inserted into the text with no manuscript evidence at all. I'd be wary of those who simply insert things or change things in Scripture for their own purposes.
Blood Transfusions Banned
One of the more interesting practices concerning Jehovah's Witnesses is that they do not believe in receiving blood transfusions, even if a transfusion would save a life. Some Jehovah's Witnesses carry a signed card that instructs someone who might find them unconscious not to give them a blood transfusion. They believe that receiving a transfusion would be equivalent to "eating blood," which is forbidden in Genesis 9:4, Leviticus 17:11-12, and Acts 15:28-29. While several Christians would agree with the proscription against eating blood, they would challenge the notion that receiving a transfusion is the same thing as "eating." Medically, the body does not receive a blood transfusion as food. Also, the Watchtower organization has changed its mind twice regarding medical prohibitions in the past. Vaccinations were banned in 1931, but allowed in the 1950s, while organ transplants were disallowed in 1967 and labeled as cannibalism, but allowed in 1980 (p. 381). One wonders if they will eventually change their mind on blood transfusions as well.
No Birthday Celebrations
Jehovah's Witnesses refuse to celebrate birthdays because of Genesis 40:20-22 (the putting to death of Pharaoh's baker on Pharaoh's birthday in the Joseph story) and Matthew 14:6-10 (the beheading of John the Baptist on Herod's birthday). Because of these two accounts, the conclusion is drawn that birthdays are evil. But the conclusion seems silly: who were the sources of evil in the accounts: Pharaoh and Herod, or birthdays? What about a birthday would be corrupting? We should be thoughtful when it comes to making a prescription out of a description in Scripture, because sometimes it's not warranted. For instance, Judas killing himself is a description of how a conflicted man took his life, but not a prescription for us to go and do likewise. Yes, Herod and Pharaoh did something bad on their birthdays. So what? That doesn't necessarily mean birthdays are wicked and inherently evil things in and of themselves.
Conclusion
The book goes into much deeper detail. I found it to be helpful for having more of a grid when it comes to knowing what Jehovah's Witnesses believe. Maybe this will help you too. If you're a Witness, I'd encourage you to read the book, and consider coming to a Christian congregation more in line with historic Christian teaching, even at the threat of being disfellowshipped by your fellow Witnesses. I'd encourage the rest of us to treat Jehovah's Witnesses with kindness and love–the whole "love your neighbor as yourself" thing. And the next time one comes to your door or you come to theirs, maybe this will give you something interesting to talk about.