Biblical Musings 10

Catapult Stones from Maccabean Times, Tower of David Museum, Jerusalem

"And I also say to you that you are Peter, and upon this rock I will build My church; and the gates of Hades shall not overpower it. I will give you the keys of the kingdom of heaven; and whatever you shall bind on earth shall be bound in heaven, and whatever you shall loose on earth shall be loosed in heaven."  Matthew 16:18,19 (NASV)

What are the implications of this statement? What is the power of binding and loosing? Who has this power?