The marriage of good and truth can be thought of as the union between our desire for good and our understanding of how to be good. This relationship is not static but dynamic; good leads us to search for truth, and truths stand independently of our changes of state, so that we can measure ourselves against them and decide to apply them in our own lives as good. This process is the basis of human regeneration.
From childhood, we are all engaged in a struggle between our hearts and our minds, between the relatively selfish things we want and the more noble things we know are right. The more we do what we know is right, the more the Lord will slowly be able to start changing our hearts, removing the selfishness bit by bit so real love can come through. This is a lifelong process, but ultimately we can reach a state where we truly love doing what's right, and our hearts and minds can be "married" so that they can work as a united whole.
Everything in creation is a form of this marriage. In human society, it can be found in many ways. It can exist inside each person individually. It can exist between a husband and a wife, since women have gifts for receiving the desire for good and men have gifts for receiving the understanding of truth. It can be forged by a group of people as a church. And it exists between the Lord as the bridegroom and the church as a bride.
When the Bible talks about marriage, marrying, and weddings, it is also talking on a deeper level about the spiritual marriage of good and truth.
(References: Arcana Coelestia 2466; Conjugial Love 44 [6])
