There is a tendency to think of the realm of God and the realm of the world in human terns, as if these were geographic designations. But there is no gate between the two, pearly or otherwise. Jesus wasn’t talking about physical barriers, but about changes of perspective.
Entering into the spirit of the game can mean different things depending on the game, because the spirits of the games are different. Entering into the spirit of a game of chess will look very little like entering into the spirit of a game of hide-‘n-seek, or a game of baseball, or a game of chance. One thing, though, they all have in common: an acceptance of the rules and acquiescence to the manners and mores of the game.
Of these, the rules are the most obvious. The pieces on a chessboard can only be moved in ways defined by the rules of chess, and to enter into the spirit of a game of chess must require, at a minimum, to abide by those rules.
The manners and mores of the game are much more nebulous, but in a way more important, and probably what we usually have in mind when we speak of the spirit of a game. The spirit of chess, to stay with our illustration, has elements of respect for the deliberation of one’s opponent. Although its practice is nowhere prohibited within the formal rules of chess, it goes without saying that whistling loudly while awaiting your next turn would not be at all in the spirit of the game. Just so, wandering without curiosity, aloof and morose, would not be entering into the spirit of hide-‘n-seek. And so on.
And what is true of games is true of most of the elements of life. To enter into the spirit of a festive holiday meal is quite different from entering into the spirit of holy communion; the spirit of neighborliness has nothing in common with the spirit of battle; the spirit of worship differs dramatically from the spirit of tyranny, and itself may look very different in different religions.
What Jesus revealed to us is what we might call the spirit of heaven, its rules, of course (which are only two ), but more importantly, its manners and mores. The many images he uses of gates and doors and precincts, the symbolic miracles, the explicit beatitudes, are all about entering into that spirit, as he himself is its embodiment.