Claim. Pledge 3 calls the family “the textbook” of the heavenly kingdom because only by experiencing all Four Great Realms of Heart — child, sibling, spouse, parent — can a person find oneness in either earthly or spirit-world Kingdom.
Elaboration. SMM is explicit about the pedagogy: “In pledge number three, we find the contents of a textbook about the heavenly kingdom in which Adam and Eve have not fallen. Everyone without exception will have to accomplish that work” (3.1. The Four Great Realms of Heart, 264-195 1994.10.9). And the prerequisite for the Kingdom: “no matter who we are, we come to establish families centering on the Four Great Realms of Heart; our families are the base for us to experience the ideal realm of heart. And just like God, only those of us who actually experience the Four Great Realms of Heart can find oneness anywhere in the Kingdom on earth and the Kingdom in heaven. This is the reason we feel drawn to establish families: we want to become such ideal human beings” (259-44 1994.3.27). Single-life religious paths are therefore disqualified: “Those who never experience a spouse’s love, who never experience a parent’s love, or a sibling’s love, or the love coming from a child, are unable to get close to God” (263-57 1994.8.16). The family is structurally the Kingdom — there is no other route.
See also. csg-four-great-realms-of-heart-are-perfected-through-marriage, csg-only-restored-families-can-recite-the-family-pledge