Matthew also wants his readers to notice that Jesus invests Peter with authority to invite into the kingdom those previously excluded. In verses 17-19 Matthew was probably trying to send a message to the conservative Jewish Christians in his congregation who didn't want to admit Gentiles. "We must defer to Peter's authority," Matthew was implying. And his decision (Acts 10) was to admit them with open arms. Who are we to contest the holder of the keys?
Peter's confession is important in its own right. From it we learn who Jesus is: the Messiah. From it we learn who Peter is and will be: Peter is the one whom God inspires to publicly confess Jesus' identity. Peter is therefore the one Jesus chooses to invest with unique authority in the movement that will come out of his ministry.
It would be easier for us to stand on the outskirts of this scene, observing Peter's reception of special status. But Peter's confession is also ours. And so is his commissioning. We share Peter's identity as flawed disciples who sometimes, in pressure situations, let Jesus down. We share in his identity as disciples forgiven and empowered by Jesus to face whatever trials and sufferings lie on the path ahead.