While going to seminary for my B.D. degree our professor used, "Four Major Cults" Wm. B Eerdmans Publishing Company, copyrighted in 1963 which included Jehovah Witnesses, Mormonism, Christian Science and yes, Adventism. I will give you a couple of serious error that they hold to that classifies them outside of the Christian church. Walter R. Martin, in his "Answer Questions On Doctrine" declares that Christians at death do not go immediately into Heaven but rather lie in the grave in a 'soul-sleep mode' until the judgment. Secondly, they believe in the annihilation of the wicked. In other words, sinners will not be put in the Lake of Fire forever as Revelation 20:14-15 indicates. At the end of time they will be merely blown, if you will, into a non-existent--never existent state. They will evaporate as though they never lived a wicked life. Thirdly, their eschatology is upside down. Of the three cults I think there are some Adventist who are really saved but like some of the Apostle Paul's communicants have fallen into a lot of theological error [I Timothy 1:19-20; II Timothy 2:17-20. They do not believe that Christians die and go immediately into Heaven. But what does God through the Apostle Paul say in II Corinthians 5:8 and Philippians 1:23? There are other errors like their view on "Investigative Judgment" but this might give us some things to evaluate. While pastor in Doylestown, Ohio I became friends with an old Adventist and I believe he was saved because of his apparent love for the Lord. But especially in 'end times events' the whole system was upside down and wrong. Berrian, Th.D.