Let me begin with the reason for sharing the Gospel by using a quote from J. Mack Stiles in his book Evangelism. He notes that “All Christians should apply themselves to think through reasons for the hope we have in Christ, reasons that sweep aside the objections and questions. But as we set out the facts of the gospel, remembering evangelism’s aim helps us to be compassionate, understanding and loving (I Peter 3:15).
“Having an aim helps us to keep our perspective on what we’re doing. It steers us toward an end. Our aim helps us remember that much is at stake: to see people moved from darkness to light, from bondage to freedom….”
Sharing the Gospel with a Mormon may be seen as ridiculous by some because they believe that Mormons are Christians and for others it is politically and socially incorrect to claim that a person of another religion who does not believe only in the Jesus Christ of the Bible will not go to Heaven.
Let me first be clear on what the Gospel is. The Gospel as contained in Romans 1-4 and I Corinthians 15 for example tells us that there is a just and Holy God who has created us and He has given us laws for life. We have broken those laws and this is called sin (Romans 3). Because we have all sinned we deserve for God to send us to Hell, a place of fire and torment, for eternity (Revelation 21:8). The good news is that Jesus Christ, the second member of the Trinity, was willing to die for our sins on the cross (Colossians 1:9-18). If we will repent of our sins and put our faith alone in Christ alone for our salvation we will spend eternity with God rather than in Hell.(Romans 10:9-13)
Mormons do not believe in the God of the Bible even though they will often use the same language to describe the god that they believe in. They believe that, Elohim, the god of this world is only one of millions of gods. They believe that God is an exalted man who was at one time like we are now. Read this and a large number of other thoughts that contradict Scripture in Joseph Smith’s (the founder of Mormonism) own words in his King Follett Discourse by clicking here. This is in direct contradiction to Isaiah 43:10 and many other passages.
They believe that Jesus Christ is the spirit brother of Lucifer and is just a man like we are and he is progressing on to become a Mormon god himself. John 1 tells us that Jesus Christ, the Word, was in the beginning with the Father. Revelation 1 tells us that He is the Alpha and the Omega, the Beginning and the End. He has existed from eternity past and will exist into eternity future. They teach that we also can progress to become gods and “know all things.” See Doctrines and Covenants 93:26-28 and Doctrines of Salvation, Vol. 1, pp 5-10.
The King James Version of the Bible is only one of their “Four Standard Works.” They will use the Book of Mormon, Doctrines & Covenants, The Pearl of Great Price, and the King James Version of the Bible “insofar as it is translated correctly.” Most of their doctrine does not come from the Bible or the Book of Mormon but from Doctrines & Covenants. When they use the Bible it is only to support their beliefs that were handed down through their prophets. They believe that “Our lives will not end when we die. Our future lives are determined by the way we live our lives now.” See Mormon Plan of Salvation.
So what does all of this add up to? It adds up to the fact that they believe in a different God, a different Jesus, a different definition of mankind, and a different way of acquiring salvation. This is why in the Great Commission that Jesus told His disciples to go into all the world and preach the Gospel. The Gospel can only be defined by the Bible and Paul takes his readers to task for believing in a different Jesus and a different Gospel.
If you are interested in learning more then please check out The Light Project. This is an 8 part series dedicated to shining the light of the true Christ on the darkness of the Cults and World Religions.
 J. Mack Stiles, Evangelism, p. 35