They were they believed separated from the wicked based on what thy believed, as evidenced by their works. "Yea, a man may say, Thou hast faith, and I have works: shew me thy faith without thy works, and I will shew thee my faith by my works." (James 2:18) Everything that we do is a result of what we truly believe - at least at the moment. While works are the criteria for determination of whether what one professes is the truth, it is not the works or our practical sanctification that make us good enough to be with God in Heaven, which is the error of Rome (thus Purgatory).
1 Simon Peter, a bondservant and apostle of Jesus Christ,
To those who have obtained like precious faith with us by the righteousness of our God and Savior Jesus Christ:
2 Grace and peace be multiplied to you in the knowledge of God and of Jesus our Lord, 3 as His divine power has given to us all things that pertain to life and godliness, through the knowledge of Him who called us by glory and virtue, 4 by which have been given to us exceedingly great and precious promises, that through these you may be partakers of the divine nature, having escaped the corruption that is in the world through lust.
Everything; eh? I guess the BoM is not needed (according to GOD's word...) I guess the D&C's are not needed (according to GOD's word...) I guess the Pearl of Great Price is not needed (according to GOD's word...)