Question: Mormons (or LDS) tell us that their Book of Mormon is “another testament of Jesus Christ.” If this is true, how can it differ from our own Holy Bible, which is believed to be the final word of God?
Answer: The Mormon claim is not true. It is contrary to constant teaching of the Church. The Catechism of the Catholic Church says, “The Christian economy, therefore, since it is the new and definitive Covenant, will never pass away; and no new public revelation is to be expected before the glorious manifestation of our Lord Jesus Christ” (No. 66).
While our understanding of completed Revelation (or the “Deposit of Faith”) may deepen, its content cannot change, be amended or receive any additions. Many, including the Mormons, err in this regard. Revelation is complete and closed with the death of the Last Apostle.
Catholic teaching on divine revelation
The Second Vatican Council teaches that Jesus Christ is the fullness of divine revelation. The council fathers write,
“Then, after speaking in many and varied ways through the prophets, “now at last in these days God has spoken to us in His Son” (Hb 1:1-2). For He sent His Son, the eternal Word, who enlightens all men, so that He might dwell among men and tell them of the innermost being of God (see Jn 1:1-18). Jesus Christ, therefore, the Word made flesh, was sent as “a man to men.” He “speaks the words of God” (Jn 3;34), and completes the work of salvation which His Father gave Him to do (see Jn 5:36; Jn 17:4). To see Jesus is to see His Father (Jn 14:9). For this reason Jesus perfected revelation by fulfilling it through his whole work of making Himself present and manifesting Himself: through His words and deeds, His signs and wonders, but especially through His death and glorious resurrection from the dead and final sending of the Spirit of truth. Moreover He confirmed with divine testimony what revelation proclaimed, that God is with us to free us from the darkness of sin and death, and to raise us up to life eternal” (Dei Verbum, 4).