Today a pair of Mormons came up to me while I was out the front of my house. They said that they wanted to tell me about how families can last forever. When they heard we’re Christians, they said that anyone who genuinely asks God to illuminate them will find that the Book of Mormon is also God’s word. My response was that the NT encourages us not only to ask for God’s illumination, but to work hard at thinking things over (2 Tim 2:7). I said that as I had thought things over, my conviction was that the NT, combined with the OT, is sufficient revelation of Jesus Christ. This is because it arises from the missions of those apostles who were appointed by Jesus as witnesses of his risen status – of whom Paul is ‘the last.’ The Mormons asked if I had a Bible reference for that. I said 1Cor 15. They asked if I had a particular verse. I cited it. This caused them to pause for a moment, but then they were back into their, ‘Ask God to make you believe in the Book of Mormon’ routine… and that’s where it ended.
I think this is an important point – as Protestants, we hold that the church has recognised (not created) the canon of the NT as Scripture that closes the canon of the Bible. The key criterion for this recognition is apostolicity – which means not that it was all authored by apostles, but that it arises from the missions of the apostles who witnessed the risen Jesus. And the last of these is Paul (not the last of the writers, but the last of the heads of mission to witness the risen Jesus).