In Matthew 13, Jesus says to His disciples: “The kingdom of heaven is like a mustard seed that someone took and sowed in his field; it is the smallest of all the seeds, but when it has grown it is the greatest of shrubs and becomes a tree, so that the birds of the air come and make nests in its branches.”
In Matthew 17, again speaking to His friends, He says: "You don't have enough faith. I tell you the truth, if you had faith even as small as a mustard seed, you could say to this mountain, 'Move from here to there,' and it would move. Nothing would be impossible."
In the mustard seed, we have a Kingdom of Heaven picture of something that starts tiny and sprouts enormously and a measure of faith whereby one can move mountains. So is faith (Belief) the whole essence of the Kingdom of Heaven? Is it the only currency with which to transact in the Heavenly economy?