Heaven comes to earth when spirit and soul collide. They collide when the atmosphere is so pregnant with joy and expectation that for a moment in time, the path of the spirit and the path of the soul become one.
Spirit and soul are not often headed in the same direction. While the secret goal of the spirit may indeed be joy, the brain usually can compel the spirit to pursue the brain's roadmap for getting to the place of joy. So the spirit is sent on wild goose chases. Perhaps for decades, it pursues relationships, possessions, recognition, the perfect physique, etc. In each, there might exist some fleeting sense of happiness that can be sustained only for a limited time.
But genuine joy results from pursuing oneness with God. Before joy takes up residence in the soul, the spirit experiences genuine joy not as the happy experience of achieving a goal, but rather, as an inner sense of unfathomable bliss that permeates every cell of one's being. The experience is fleeting. It lasts perhaps for a few hours or a few days at the height of a spiritual journey. It is fleeting not because the experience is now in the past, but rather, because the true experience has not yet arrived. It is a taste of heaven, a touch of God that leaves us with an insatiable craving for more, for that moment when heaven again comes to earth.