The Godhead is the Antetype of the Family

The Godhead itself, mysterious and unsearchable as it is, is the fore-shadowing, the antetype of the family. Man is said to be created in the divine image;  but the combined man, which constitutes the family, far more than the solitary man or woman, is the true image of God. And the reason is, "God is love.” And if he is so, then there must have been an eternal Beloved. Otherwise, he would have been the most miserable of beings. Absolute solitude is inconsistent with happiness. What could be more miserable than a being, the very essence of whose nature is love, without an object to meet and to satisfy its unalienable and mighty tendencies? And that object, to meet the ends for which it exists, must be as infinite as the love of which it is the subject.  And if it must be infinite, because nothing short of infinite would be an appropriate object of the divine affections, it must also have been eternal, because otherwise the divine affection, through countless ages, would have had no object at all. And hence, there is, and must be, innate in the Godhead, the infinitely beloved, the Chosen and Anointed of the Father, the Eternal Word, the Immanuel. But this duality of existence, which is constituted into unity by the unchangeable bond of the affections, cannot be perfectly happy except in some object possessing a like infinity of character, which may be regarded, speaking after the manner of men, as "a procession or emanation" from the two. And this re-production of itself, infinite in its nature, perfect in its love and by "an everlasting generation," constitutes and completes the adorable family of the Trinity.

Man, created in the divine image, is male and female; and these two are one. And their united existence, deriving a new power from their union, multiplies and images itself in a third, which is also a part of itself. It is man, therefore, in his threefold nature, — the father, the mother, and the child,— the beautiful trinity of the family, and yet so constituted that in man's unfallen state it would never have suggested the idea of a weakened or discordant unity, — which may be regarded as the earthly representation, the visible, though dim,  shadowing  forth of the divine personalities existing in the unity of the Godhead. The original type is in the infinite; but it is reproduced and reflected with greater or less degrees of distinctness in all orders of moral beings. 

— edited from A Treatise on Divine Union (1851) Part 7, Chapter 6.