Believing — Mormons believe a very important principle of the gospel is faith.
Behaving — We also believe we are not saved by faith alone, but also by works, as well as grace and other necessary steps. James 2:14 reads, "What doth it profit, my brethren, though a man say he hath faith, and have not works? Can faith save him?"
And from the Book of Mormon, Moroni 10:32 says, "Yea, come unto Christ, and be perfected in him, and deny yourselves of all ungodliness; and if ye shall deny yourselves of all ungodliness, and love God with all your might, mind and strength, then is his grace sufficient for you, that by his grace ye may be perfect in Christ; and if by the grace of God ye are perfect in Christ, ye can in nowise deny the power of God."
Belonging — We believe baptism is a necessary ordinance for salvation. That's part of why we practice genealogy and baptism for the dead. We believe it's an ordinance that must be performed on earth on behalf of every soul, whether that soul chooses to accept it or not. We believe everyone will at some point, (if they didn't in this life, then in the next) get a (good, complete, fair) opportunity to learn about the gospel of Jesus Christ if they don't now have it.