As, in the structure of the world, the apparently opposing tendencies of the centrifugal and centripetal forces produce the harmony of the spheres, so, in the social life of man, self-interest and conscience produce in him the feeling for the common good.(108) This sentiment of the common interest is the foundation on which rise in successive gradation, the life of the family, of the community, of the nation and of humanity, the last of which should be coincident with the life of the Church. It, alone, can realize the kingdom of heaven on earth. Through this sentiment alone can religion be made active and moral. Only through it, can self-interest be made really sure and always to the purpose. Even the most calculating mind must acknowledge, that numberless institutions, relations etc., are useful and even necessary to many individuals, which can be established or maintained only from a sense of the general welfare, for the reason that no one individual could make the sacrifice required to establish or maintain them. And so, since commerce has wrought the interests of all men into one great piece of net-work, the best means of obtaining wherewith to satisfy our own wants is to help others satisfy theirs. Self-interest causes every one to choose the course in life in which he shall meet with the least competition and the most abundant patronage; in other words, that which answers to the most pressing and least satisfied want of the community. As a rule, the physician who cures the greatest number of patients with the greatest skill, and the manufacturer who produces the best goods cheapest, will grow to be the richest. It is, moreover, easy to see that, according as the circle of common interests grows smaller, it approximates to self-interest; and to “the Kingdom of God”(109) as it grows larger. And yet, all these circles respectively condition one another. Cosmopolitanism or church-zeal, without love of country; patriotism, without fidelity to the community in which one lives, or love of one’s family, are more than suspicious. The reverse is also true. This is a chief connecting link between the great apparent opposites.(110)(111) Section XII. Economy.—Grades Of Economy. Thanks to this feeling for the common weal, the eternal and destructive war—the _bellum omnium contra omnes_—which an unscrupulous self-interest would not fail to generate among men engaged in the isolated prosecution of their own economic interests, ceases in the higher, well-ordered organization(112) of society. On it are based the various forms of economy in common: family-economy, corporation or association-economy, municipal economy, and national economy.(113) And these forms of economy in common are so essentially the condition and complement of individual economy, that the latter, without them, could either not be maintained at all, or, at least, only in the very lowest stage of civilization.