"God created the world for his Son, that he might prepare a spouse or bride for him to bestow his love upon; so that the mutual joys between this bride and bridegroom are the end of creation" (Works, 13, p. 372; Misc. no. 271).
"This spouse of the Son of God, the bride, the Lamb's wife, the completeness of him who filleth all in all, that for which all the universe was made. Heaven and earth were created that the Son of God might be complete in a spouse." (Misc. no. 103).
That last quote will sound heretical in some ears - that the Son of God was incomplete without a Bride, but I think (and others may have better answers) the point is not that the Son of God is deficient in some way until he receives the church - I was single for the best part of 33 years, but never considered myself sub-human as a result - rather that love finds its ultimate expression in giving and sharing. And so in drawing the church up into the life of God, Christ gives new and fuller expression to the perfect love that has eternally flowed from him.
Sometimes you just have to say there is a beautiful mystery to all this...