But the difficulty with sharing Christ with Jehovah's Witnesses isn't the information, but the receptivity. It can be a frustrating experience for the immature or the mature Christian. Yet, there is really only one issue that needs to be dealt with if any headway is to be made.
A Jehovah's Witness is trained to defend preconceived ideas and challenge established Christian theology. They have no interest in what you have to say, because you are deceived. Therefore, they are predisposed to not listen to any reasoned argument if it doesn't reflect the Watchtower organization's point of view. Being fully devoted to the Watchtower organization's theological framework they are willing to reinterpret and twist Scripture to agree with the Watchtower.
What makes it more difficult is that they are fully convinced in their own minds that mangling Scripture isn't what they are doing. Instead, they believe that the Scriptures teach what the Watchtower believes. However, when they prove this point they will jump from passage to passage with no regard for context to justify this notion. Then they claim that their way of interpreting Scripture is the norm. "See the apostles use different Scriptures to make their point." What they ignore is that apostles and prophets are clearly ordained by God through visible power and special appointment by Jesus, or God himself, while our goal is to understand what they taught. (The difference between inspiration and perspiration.)
Another issue that makes it very difficult to share with them is that they are willing to tell half-truths, or even lie, to convince people that what they are saying is true. They call this spiritual warfare. The idea is that since Christians are deceived, it is okay to employ this tactic in order to get them to acknowledge their truth.
What's the best approach?
Well, how do you share with people who do these types of things? Ignoring them certainly isn't going to much effective. (Although, there are times when this is the best approach.) When Christians choose to engage a Jehovah Witness, there really is only one problem to deal with. Rather than going through bunny trails and endless debating, just ask them to explain one issue: "Why do you trust that the Watchtower speaks for God?" That really is the issue, isn't it?
Although Witnesses may counter with statements such as, "They only speak what the Bible says", "They don't speak for God, they merely interpret what God said", or even, "Don't you use trusted sources to help you interpret the Bible?", it doesn't matter. Find out why they trust the Watchtower organization (these few men) for themselves—as individuals. Did the men in the Watchtower organization do something to illicit this trust? How can you know what they say matches the Scriptures, if you need them to explain the Scriptures? If they aren't prophets or speak for God, how can they have the authority to teach on extra-biblical theology such as the nature of the Spirit, celebrating birthdays, and so on? And if they are ordained to speak for God (as prophets), how were they ordained and what's the proof?
I've found many times that Jehovah's Witnesses place their trust in the Watchtower organization (men) because they feel deep down inside that these men are telling them the truth. Some have even said that the publications, the Watchtower produces, says that they are telling the truth. (I kid you not.) So the next question is an obvious follow-up: "So, if I told you that I am telling you the truth from God, then why don't you believe me?" Some get the point, while others choose to ignore the problem. But either way, the true issue is exposed, rather than engaging in endless debating.
Whatever happens next really doesn't matter, because the problem still remains: the Jehovah's Witness has her trust in a few elders in a N.Y. office called the Watchtower for no good reason, other than she has chosen to. It is incumbent upon the Witness at your door to demonstrate why you should believe that too.