Apostasy occurs when a Mormon turns away and rejects the commands and ordinances of the LDS gospel. The consequence is even greater if a Mormon makes covenant promises with God in the temple then chooses to break them by leaving the LDS Church. This action is considered an unpardonable sin against the Holy Ghost and punishable by eternal death in outer darkness, thus becoming a “son of perdition.” An inactive Mormon (also known as a Jack Mormon) who struggles to keep the commands is not considered an apostate.
The Great Apostasy in Mormonism describes the time between the death of the biblical apostles and when Heavenly Father and Jesus Christ appeared to Joseph Smith in 1820. Mormonism teaches that the fullness of the gospel was restored after being corrupted and lost with the establishment of the LDS Church.
The LDS Church warns Mormons to stay away from apostate groups or anti-Mormons who attempt to discredit the Church and its teachings. Mormonism teaches that one of Satan’s primary objectives is to steal or ruin their testimony. For this reason, anybody who shares the truth of God’s Word or discredits a Mormon’s faith is an agent of the devil.