The first two parts of John’s message are sin and the need for forgiveness, and the person of Jesus Christ. The third part is the work of Jesus Christ. The third and last part of John’s message points to the work Jesus was coming to do, and that was to achieve our salvation. In Mark this is summarized by the contrast between John’s preparatory work and the greater and more effective work to be done by Jesus. John says, “I baptize you with water, but he will baptize you with the Holy Spirit” (v. 8).
To be baptized with the Holy Spirit does not mean what many people take those words to mean today. That is, John was not promising that Jesus would impart a so-called second work of grace so that those who had been baptized by John would begin to speak in tongues, do miracles, or any other such thing. What he was talking about is what Jesus himself was talking about when he told Nicodemus, “You must be born again” (John 3:7). The point is that John could do an outward baptism, like any other mere human being. But what is needed is an inward baptism, which is the gift of a new nature, and the only one who can do that necessary, supernatural work is the divine Savior.
That is not the only way John explained the work of Jesus, of course. Mark is giving us a very brief account. But we know from John’s Gospel that John also pointed to Jesus as “the Lamb of God, who takes away the sin of the world” (1:29)! That is, he also explained Jesus’ work by pointing to his coming death on the cross.
Calling Jesus “the Lamb of God” would have been very meaningful for John’s listeners. This is because the Jews knew about the sacrificial lamb and had been sacrificing lambs for centuries. They had learned about this first from the story of Abraham, the father of their nation. At God’s command Abraham had been going up Mount Moriah to sacrifice his son Isaac, when Isaac had turned to his father and asked, “Father?…The fire and wood are here, but where is the lamb for the burnt offering” (Gen. 22:7)? Abraham had answered, “God himself will provide the lamb for the burnt offering, my son” (v. 8).
I call that exchange the very heart of the Old Testament and even of the entire Bible. For it was both the expectation and hope of the Old Testament saints. It was the promise of the Savior to come. By itself the offering of sacrifices pointed to the way of salvation. That is, the sinner has sinned against God and deserves to perish for his or her sin. But God has shown that it is possible for an innocent victim to die in the place of the sinner. When Adam and Eve sinned, one animal was sacrificed for Adam and another was sacrificed for Eve. Similarly, a lamb had been killed in Egypt on the night of the Jewish escape from that country, one lamb for each Jewish family. And later at Mount Sinai God revealed that one animal could die on behalf of the entire nation. Every Jew understood this symbolism.
But that was just the trouble. It was only symbolism. It pointed to the way of salvation, but anyone with any understanding knew that an animal was not the equivalent of a human being. Therefore, although the sacrifice pointed to the sacrifice that was to come, it was not that sacrifice, and the world waited (or should have been waiting) for the true Redeemer.
When Isaac asked, “Where is the lamb?” he was asking the single most profound question of the Old Testament or of religion as a whole. And when Abraham answered, “God himself will provide the lamb for the burnt offering,” he was giving the most profound answer any Old Testament figure could have given, until Jesus Christ actually came. But now he has come. So when John the Baptist pointed to Jesus saying, “Behold, the Lamb of God, who takes away the sin of the world,” he was saying that the time was fulfilled, that the Savior has come, and that salvation from sin is to be found in trusting Jesus as the one, only, and all-sufficient Savior.