What is the tenets of the Seven Day Adventist system of Christian belief?

The Modern Adventists are not any different the the vast majority of Protestant churches. With the exception that they worship on Saturday (the Biblical Seventh day Sabbath). I, however, am Not a Modern Adventist, I am a Founderest. That means that I believe the same as the Founders of the SDA religion, which is quite different then what the Moderns believe (the changed our religion in 1958) and they are now advocating Sunday worship! Can you believe such a thing? I wish to know: why would a Seventh Day keeper religion change their religious practices? It make no since except in one way: they are preparing to follow the Beast and the Anti-Christ.