As a preface to this answer, please see our article on Mormonism and what Mormons believe. As Christians, we always want to use the Bible and its timeless truths as our primary tool in witnessing the love of God and salvation through Christ. One of the problems with trying to witness to Mormons is that they believe that the Bible was hopelessly corrupted through the years and is no longer reliable. Although we can say with confidence that the Scriptures are most certainly not corrupted—due to the manuscript evidence in the form of the Dead Sea Scrolls, several codices of the various portions of the biblical text, and thousands of other manuscripts—Mormons are most likely not going to agree to that. Therefore, approaching Mormons from another direction is more effective.
It is important to understand that Mormons use many of the terms that Christians use, such as salvation, justification, heaven, and others. But their definitions are quite different from the biblical definitions we are familiar with. For instance, Mormons say they believe in salvation by grace through faith in Christ. But their idea of salvation is inclusive—everyone has been saved by Christ so that they will live eternally, but it is each person’s works that will determine where they will spend eternity and the extent of their eternal blessings (Articles of Faith, p. 78–79; Mormon Doctrine, p. 348). Clearly, salvation as the Bible explains it is not the same as the Mormon idea of salvation. This is why arguing doctrine with a Mormon is rarely successful.
The key to reaching the heart of Mormons is to understand that, while they may appear confident and self-assured on the outside, internally many are filled with stress and doubt because they are continually striving for perfection. This is partly driven by Mormon doctrine and partly by family pressures. Family is extremely important to Mormons, and living up to both family and church standards is a motivating factor to many Mormons. Deep down inside most Mormons is the fear of not being good enough, of not measuring up. The question in every Mormon’s mind is, “Am I worthy enough?” The best thing to do is to reinforce that doubt. Show them that by their own efforts, they are not even close to being worthy to stand before a holy God. This is the bad news that has to precede the good news. Show them from the Scriptures that all their “righteous acts are like filthy rags” (Isaiah 64:6), that “no one will be declared righteous in his sight by observing the law” (Romans 3:20), and that “all have sinned and fall short of the glory of God” (Romans 3:23). If the Mormon will admit to these truths, he/she should be open for the good news of the true gospel of Jesus Christ, that real righteousness only comes at the cross, where God exchanged our sin for the righteousness of Christ (2 Corinthians 5:21). No other righteousness can stand before God on Judgment Day. Once a Mormon, or anyone else for that matter, admits these truths, he/she is well on the way to understanding true salvation.
While it is important for us to be diligent in our proclamation of truth, it is also important for us to put the results of witnessing in the hands of our God, who is able to “save to the uttermost those who draw near to God through Him” (Hebrews 7:25). We can rest assured that, ultimately, it falls upon the Spirit to sway the hearts of those who are lost and open their eyes to Truth. Our job is to “always be prepared to give an answer to everyone who asks you to give the reason for the hope that you have. But do this with gentleness and respect” (1 Peter 3:15), trusting God with the words that we are to say, praying diligently for the souls of those we witness to, and leaving the results to Him.
(Editor’s note: many of the references in our articles on Mormonism are Mormon publications, such as Mormon Doctrine, Articles of Faith, Doctrines of Salvation, History of the Church, Doctrine and Covenants, and so forth. Others are from the Book of Mormon itself, e.g., books such as 1 Nephi, 2 Nephi, and Alma.)