Even the most diligent followers of Christ fail at times to believe His Word, as we see in the case of the original disciples (Mark 16:9–13). Yet our gracious Lord does not view that sin as disqualifying us from serving Him, provided, of course, that we repent of our doubt and ask Him to help our unbelief (see 9:24). We see this in the longer ending of Mark’s gospel, for Jesus commissioned the same disciples who did not initially believe Jesus rose from the dead to “proclaim the gospel to the whole creation” (16:15). Christ’s followers must preach the gospel to all people—rich and poor, men and women, old and young, educated and uneducated. Everyone of every social class and ethnicity must hear the message of salvation.
The rest of Mark’s gospel provides clues as to what Jesus means by “the gospel.” First, it is the proclamation that Jesus is the Son of God (1:1; 15:39). Proclaiming that Jesus is the Son of God means declaring that He is truly God and one with His Father, possessing the same abilities and authority as the Father (2:1–12). The Son is true deity, not some lesser divine being. Furthermore, the gospel says that Jesus came to give His life as a ransom for many, to pay the price for their sin, and was raised from the dead to prove that His sacrifice is accepted by God as the perfect atonement for transgressions (8:31; 10:45). Finally, proclaiming the gospel involves calling people to believe in Jesus and to prove this faith in a life of discipleship (8:27–37). In sum, Dr. R.C. Sproul writes in his commentary Mark, the gospel “is the announcement of the person and the ministry of Jesus, and of how the benefits of His life and death can be appropriated by faith.”
Let us not fail, however, to tell people that how they respond to the proclamation of the gospel is the most consequential decision they will ever make. The one who believes it and is baptized will be saved forever. The one who dies without believing the gospel will be condemned for all eternity (16:16). Baptism is here mentioned with faith because the New Testament connects the two very closely, but they are not connected in an absolute way. In other words, the act of baptism in itself confers no saving benefits apart from faith. Moreover, like the thief on the cross, it is possible to be saved without being baptized (Luke 23:39–43). Yet, this does not make baptism optional. To be saved without being baptized is an extraordinary circumstance. If we refuse to be baptized, we show an unwillingness to obey Christ, which indicates that we do not trust Him (John 14:15).