What does Mark 3:16 mean?

From this point on, the Gospel of Mark typically refers to the apostles as "the twelve." The word translated "appointed" comes from the Greek root word poieo. It implies more than simply selecting something; it means to make something. When Jesus selects the twelve, He makes a core unit of teachers and representatives that will soon become the nexus of the church. It means more than a new calling—it means a new identity.

In this verse, Peter takes pre-eminence over his brother Andrew and the other disciples (Matthew 10:1–4; Luke 6:13–16). His Hebrew name, "Simon," is a variation on Simeon and means "hearkening" or "hearing." In some parts of the Bible he is identified by his name in Aramaic, Cephas (John 1:42). Jesus renames him Peter—translated Petros in Greek—Cephas in Aramaic (John 1:42), which means "rock" or "stone."

There is some confusion about this nickname. In Matthew 16:18, Jesus says He will build His church upon "this rock," which some interpret as a reference to Peter. This is the justification Roman Catholics give for the office of Pope. In a practical sense, there is some truth to the interpretation that Peter is the rock, since Peter is the first to bring Jesus' teaching to the Gentiles (Acts 10:1–48). But it's far more faithful to the context to assume Jesus means His church will be built on the rock of Peter's statement in Matthew 16:16: that Jesus is "the Christ, the Son of the living God." This is all the more likely, since Jesus uses two subtly different Greek words, with two different meanings, in Matthew 16:18.

Peter is by turns bold, brash, careless, and cowardly. He identifies Jesus as the Messiah one moment, and foolishly tries to keep Jesus from His work the next (Mark 8:31–33). He tries to protect Jesus from being taken by the scribes to be killed (Mark 14:46–47) and mere hours later denies he knows Jesus (Mark 14:66–72). After the resurrection, he is so excited to see Jesus he swims to Him instead of taking the boat (John 21:7), but takes years to understand some of Jesus' more challenging teaching (Acts 10:9–43; Galatians 2:11–14).