The Kingdom of Heaven is ever-present. Hence, it is always available to be experienced. Then why doesn't it seem more evident? Because it is not appreciable to sick and sinful mortal thought. Then how does one perceive and gain the Kingdom of Heaven? Two of Christ Jesus' parables in particular, juxtaposed in Matthew 13: 44-46, answer that question: the treasure in the field and the pearl of great price.
It is perhaps worth noting that the man who stumbles on the treasure in the field does not simply sneak off with it, but re-burys (the KJV says hides) it. Then he sells all that he has and buys the field. No doubt many men and women desire the Kingdom of Heaven, but only if they can get it on the cheap. It apparently isn't worth to them "all that they have".
What does it mean to sell all that one has and buy it, since it is certain the Kingdom of Heaven cannot be bought with money? Here J. R. Dummelow's Commentary is most helpful. "Their teaching [those two parables] is that it is not enough to be outwardly a Christian or to be under Christian influences. The true Christian must be inwardly convinced that his religion is the most precious of all things." To buy the field the man "sells all that he has, i.e. gives up all that can hinder him in his quest . . . ." To buy the pearl of great price the merchant "Selleth all that he hath] i.e. gives up every sin or self-indulgence which hinders him from giving himself wholeheartedly to Christ."
"Christian Science may be sold in the shambles. Many are bidding for it,--but are not willing to pay the price." (Mis. 269: 25-26) "Seek Truth, and pursue it. It should cost you something: you are willing to pay for error and receive nothing in return; but if you pay the price of Truth, you shall receive all." (Mis. 342: 24-27)