Material things have closed boundaries; they are not accessible, cannot be penetrated, by things outside themselves. But one's existence as a spiritual being involves being and remaining oneself and at the same time admitting and transforming into oneself the reality of the world. No other material thing can be present in the space occupied by a house, a tree, or a fountain pen. But where there is mind, the totality of things has room; it is "possible that in a single being the comprehensiveness of the whole universe may dwell.