Over our vacation, we spent a couple downs in Bloomington with some friends, one of whom is also a pastor in an RP church. That Sunday night, who would ring the bell but a couple Mormons. I am by no means a great thinker or debater, but two pastors and two Mormons? It's like providential batting practice. We had them there for about 40 to 50 minutes. Here are some things I tried and learned; some of this I already knew, some was new revelation.
1. Mormon elders are extremely well-trained, but there's a limit to their capabilities (as there should be when operating in an untrue system). When you hit their limit, when you catch them, they have their fallback: "This is what I know: I had an experience, I've been convinced in my heart that this is true." Once again this lays clear the truth that I cannot convert anyone with perfectly reasoned arguments because only the Spirit changes wills...not that it's not fun or useless to beat them, though.
2. The god of the Mormons is a capricious, changing god. This was fairly new to me. Somehow we got on the topic of polygamy and they reported that the official Mormon doctrine had changed over the years. This I knew; what I didn't know was that the church claims that such changes come from god. So, the book of Mormon forbids polygamy; but ten years after its publication, Joseph Smith gets a new revelation from god, saying that polygamy is okay for a while. Recently, the high prophet got another revelation from god, now condemning the practice of polygamy. All this they reported with a smile on their face, oblivious to the implications of serving a changing god. Here I interjected Numbers 23:19 - God is not a name that He should lie, nor a son of man that He should change His mind. Does He speak and not act? Does He promise and not fulfill? - "Don't you see, guys? Your god could wake up tomorrow and decide all that stuff about salvation? I've changed my mind...all that stuff about loving you? Now I hate you. And the very changeable-ness of your god is proof of a false system. Just like little kids continuing to invent lies to support past lies, so the Latter Day Saints must continue to reinvent god to keep up with their false system."
3. In the end, the most tragic part of the night was our realization of that these two guys were trusting in their own works for salvation. They wouldn't say this, of course, but when we pressed them on it ("why will God let you into heaven?"), they mentioned both faith in Christ and a life lived as best they could - in fact, they often said things like, "We live as best we can so we can please god." This is not new - it's the same mistake most other religions have made: earning your own salvation. It is a sad thing. We spoke to them about the purpose of the law (not to measure up, but to see that we can't measure up and to draw us to Christ). We talked about the importance of properly-placed obedience (not to be made new, but because we are new). In the end, we passionately invited them to come to Christ for salvation apart from their good works, apart from their self-salvation.
4. I began the conversation by asking them what they thought about Jesus, which generally gets to the heart of the matter in conversations like this. "Do you believe Jesus is God?" I asked. "Jesus is god," they replied. "Do you believe he is the God, the second person in the Trinity?" "Uh, no. We don't believe in the Trinity. We believe Jesus is a god." This comes up with the JW's as well as many other false religions. If Christ is not God, the second person of the Trinity, there is no hope, no possibility of salvation.
5. Revelation is, obviously, a big issue. They do not believe in (1) the sufficiency of Scripture or (2) the inerrancy of Scripture. To prove this, they pulled out an extremely weak argument from John where an event is described in 2 slightly different ways (I can't remember the exact place). Anyhoo, they also believe the Book of Mormon had many mistakes, initially, but that they're all fixed now. But the problem remains of additional revelation. If the Bible wasn't enough, how can we be sure the book of Mormon is enough. Besides, Peter says the Scriptures we have are the "more sure prophetic word" which we should desire over any miracle or new revelation. What I tried to get across is the danger of receiving & wanting new revelation - it makes for a faith built on sandy ground.
Those are some of the things that came up; it was good to get a chance to proclaim the gospel in love to them and to pray for them later. Many of you know there are numerous other beliefs and practices of the Mormon church that could warrant disagreement, but I think it's important to stick to the facts of the gospel rather than trying to get them on baptism for the dead, etc.