There are two traditional answers to the question of who or what was the rock Christ referred to in Matthew 16:18. Some Christians believe that Jesus was speaking to Peter, and so Peter is the rock the church would be built upon. Other Christians believe that because the Greek word for the “rock” the Church would be built upon is petra – a “large rock” or “foundation” – and Peter’s name was petros, meaning a small rock or pebble in Greek – Christ could hardly have been speaking of Peter and must have been speaking of himself when he said “on this rock ….” (see Ephesians 2:20, etc.).
But there is another possibility which perhaps fits the context of this verse better than either of these two options, and which may be closer to the true meaning of Jesus’ words. When we look at the context of Christ’s saying, we find it was part of a larger conversation he was having with Peter:
… Jesus … asked his disciples, “Who do people say the Son of Man is?” They replied, “Some say John the Baptist; others say Elijah; and still others, Jeremiah or one of the prophets.” “But what about you?” he asked. “Who do you say I am?” Simon Peter answered, “You are the Messiah, the Son of the living God.” Jesus replied, “Blessed are you, Simon son of Jonah, for this was not revealed to you by flesh and blood, but by my Father in heaven. And I tell you that you are Peter, and on this rock I will build my church, and the gates of Hades will not overcome it. I will give you the keys of the kingdom of heaven; whatever you bind on earth will be bound in heaven, and whatever you loose on earth will be loosed in heaven.” Then he ordered his disciples not to tell anyone that he was the Messiah (Matthew 16:13-20).
The conversation begins and ends with the concept of Christ’s identity – Jesus first asks his disciples who people thought he was, and who they thought he was, then, after discussing the answers they gave, he closes the discussion by telling his disciples not to tell people who he was. When we keep this clear context of the conversation in mind, we see the subject of the whole exchange was “Who is Jesus?”
The crux of the conversation occurs when Peter volunteers “You are the Messiah, the Son of the living God” (Matthew 16:16), and it is then that Jesus confirms this assessment with an exclamation that can be summarized as “exactly!” Jesus then told Peter that this was the “rock” or “foundation” – we might say “foundational truth” – on which his Church would be built: the fact that he was the promised Messiah, the one through whom salvation would come.
Jesus also continued with another thought about binding and loosing, probably meaning that his Church would have the power to interpret the laws of the Bible in a manner similar to the “binding’ and “loosing” power the rabbis of that age exercised to permit or forbid things (to interpret the Scriptures rather than to make new laws or annul old ones). But the fact that the focus of this statement was not entirely Peter is clear in the fact that later, addressing all the disciples, Jesus repeated the same words, “Whatever you bind on earth will be bound in heaven, and whatever you loose on earth will be loosed in heaven” (Matthew 18:18).
Whatever the exact nature of the “keys of the kingdom of heaven” and the “binding and loosing” was, Jesus returned to the subject of their discussion and closed the conversation by stressing that although he was indeed the Messiah – a fact that would form the basis of his Church – the disciples were not to reveal that truth until the time was right.