Remnant church question

I attend an SDA church, but I struggle to understand some of the doctrines. I've heard it said many times (especially online) that the SDA is the remnant church of Revelation. Is it believed in the SDA denomination that it is exclusively the remnant church, or that they are part of the remnant along with other commandment keeping Christians? Also, why even make it one of the fundamental beliefs that one must affirm to join the church? Thanks.