In a marriage two people come together and unite their lives. In doing so they move in with each other - they effectively give each other keys to their house. Yet not just their house - their whole lives, their bodies, everything. Marriage is mutual invitation from one to another to fully come into their life.
In Matthew 16 Peter makes the declaration 'You are the Messiah, the Son of the Living God'. Jesus affirms this response, and basically says: "We can build on this!". Continuing the affirmation Jesus goes on to say that he will give Peter the keys to the Kingdom, kind of saying 'whatever I have ... is fully open to you'.
Marriage between two people is a kind of picture of how God wants us to be united with Him. In that union Jesus will gives us the keys to all He has! When we decide to follow Jesus, we invite Jesus into our lives (we effectively give Jesus the keys to our life). In return Jesus invites us into His life, and gives us the keys to His Kingdom.
Think about that for a moment - it's huge! With the keys to the Kingdom in our hands it means we can declare Kingdom things in the world around us, with the people we work with etc.
That is the simple truth and affirmation for us to think about this week. It has only taken a few sentences to spell out, but it has massive implications for each and every one of us as followers of Jesus.
In Jesus he has given us the keys to all He has!