Jesus asked His disciples (Matt. 16:15), “Who do you say that I am?” On that occasion, Peter by divine revelation answered (Matt. 16:16), “You are the Christ, the Son of the living God.”
If Jesus is who the Bible portrays Him to be and who He claimed to be—the Christ (Messiah), the Son of the living God—then the only sensible response is to trust Him as your Savior from sin and judgment and to follow Him as your Lord.
If He is not who the Bible portrays Him to be, then you’re wasting your time being a Christian, because you’re following a fictional character. “Who do you say that I am?” is the crucial question in life!
The apostle John was perhaps thinking of Peter’s confession when he told us why he wrote his gospel (John 20:30-31): “Therefore many other signs Jesus also performed in the presence of the disciples, which are not written in this book; but these have been written so that you may believe that Jesus is the Christ, the Son of God; and that believing you may have life in His name.”
John is not trying to persuade you to believe in some general notions about Jesus, such as, He was a good man, a great teacher, or even a prophet of God. John wants you to believe specifically that Jesus is the Christ—the Jewish Messiah (Anointed One)—who was prophesied of in the Old Testament. And he wants you to believe that Jesus is the Son of God, which means, He is God in human flesh (5:18-29). The pinnacle of faith in John’s gospel is when Thomas sees the risen Jesus and proclaims (20:28), “My Lord and My God!”
John wants us to know that in Jesus, we see the unseen God. In John 1:14, John declares of Jesus, “And the Word became flesh, and dwelt among us, and we saw His glory, glory as of the only begotten from the Father, full of grace and truth.” In 1:18 he adds, “No one has seen God at any time; the only begotten God who is in the bosom of the Father, He has explained Him.” Or, as Jesus tells Philip (14:9), “Have I been so long with you, and yet you have not come to know Me, Philip? He who has seen Me has seen the Father; how can you say, ‘Show us the Father’?”
So John wants his readers to know who Jesus is and to believe in Him as He is. The result of believing in Jesus as the Christ, the Son of God, is that you will have life in His name. By “life,” John means “eternal life.” Since the alternative to eternal life is eternal judgment, it is crucial that you know who Jesus is and that you put your trust in Him as Savior and Lord.