Well this present kingdom(till JESUS returns and included his reign). The church started off small and now it is big(just like the mustard seed) and there are other religions considered as CHRISTIANDOM which are not and it is up to CHRIST in the end to get rid of the tares among the wheat. These kingdom of heaven parables are not the goody goody thing that everyone thinks they are. You have two groups in this section of Matthew: the multitude(Those with no ears to hear and no eyes to see) and the diciples (who represent GOD's people).The multitude will never understand these parables and JESUS explains them to the diciples how to interpet them in Matt. chapter 13,the parable of the sower. You see the Kingdom (this present day) there are Non believers and satans people (Tares in the wheat) masked by all other christian organization,they are the birds perched in the large mustard tree(the fowl that take the seed in the Sower parable).When Christ comes in his second coming he is going to change all that with his glorious rule in the millineum. You notice the LEAVEN was HID,what is there to hide,our salvation or GOD's great gift to the world I THINK NOT.