So if the church of the devil isn’t any specific denomination, is the church of the Lamb of God a specific denomination or not? I don’t know. Maybe somebody else has a reference, but I can’t find anything that states one way or another. But I would speculate that the church of the Lamb of God, at least the one referred to in 1 Nephi 14:10 is not the Mormon church, nor that it refers to any specific denomination, because Mormons certainly do not believe and are not taught that anyone who is not a member of the LDS Church is automatically a member of the church of the devil.
It is my opinion that, simply put, good people are members of the church of the Lamb of God, and bad people are members of the church of the devil. And since nobody is 100% good or bad (other than Christ who was 100% good), it could even be said that the two churches are not so much made up of specific people, but rather people’s individual actions support either one church or the other. It could then be said that what God expects of us is to try our best to build up the church of the Lamb of God, and do our best to not contribute to building the church of the devil.
Not only does this conform to what is taught within the LDS Church but it is also how the LDS Church acts. The LDS Church is more than just friendly with many other religions, but cooperates extensively with other religions to provide charitable and emergency relief services worldwide. Mormons are taught never to condemn others, but to love and serve others and where possible, share what we believe. Not in order to prove anyone else wrong, but in case others are interested in learning more about what we’ve got. This isn’t to say that some members of the LDS Church might behave inappropriately and condemn those who belong to other religions, but if they do then they’re violating teachings from the Bible, the Book of Mormon, and they have a serious misunderstanding about LDS Church doctrine.