He takes on the "justice" argument for same-sex marriage in the church, which he sees as resting on a shaky premise. Basically, the church advocates of SSM are saying, "Since we are all equal in God's eyes through baptism, it is unjust to deny any baptized people access to any of the other sacraments, including marriage." (Dan gives a much more detailed explanation of the premise - I am only paraphrasing here).
Dan then goes to what should be the source for an Episcopal Church view of marriage, which is the marriage rite in the Book of Common Prayer and its explicit Biblical reference points:
However, this premise rests on a shaky foundation. It slices off and isolates one facet of what marriage is--a relationship of mutual companionship--and invests it with a life of its own, decontextualized from the whole institution of marriage. It neglects the Church's theological conviction that marriage was "instituted by God in creation" (BCP, p. 423, emphasis added); marriage is no mere human social construct that we are free to tamper with as seems expedient, but is part of the given fabric of who we are as human beings. Moreover, it is inherent to the given character of marriage to be ordered by the gender polarity (what some have called sexual dimorphism) that is also "from the beginning"--i.e. "male and female created he them" (Genesis 1:27). The fact the people (with the rarest of possible exceptions) come in two varieties--male and female--is not an insignificant datum of biology, but rather a highly significant datum of Divine design.
Then there is what we might call the "cosmic" dimension of marriage, laid out for us in Ephesians 5 (21-33) and referenced conspicuously in the aforementioned preface to the Prayer Book marriage rite. Christ (ascended and glorified but still very much the "man" Jesus) is the bridegroom and the Church is his ... wait for it ... bride--not generic partner or companion, but bride.
Perhaps the most obvious reason for not uncritically granting the premise that any pair-bond between non-related mutually consenting adults is an appropriate candidate for the institution and sacrament of marriage is what is arguably still the principal social end of marriage, which is to provide a stable environment for a pair-bonded couple to raise the biological offspring of their relationship to adulthood with as few risks as possible...
This certainly doesn't close the issue of why a secular government might impose SSM on a community, but it shows why the Christian Church should not participate when that happens. The Church ends up having to accept a false premise (actually, a whole truckload of them) by ignoring or dumping its own Scripture, tradition and reason. Once this is done for a faction - in this case, pretty much a few hundred white, middle aged-and-older LGBT Episcopal clergy and activists who want ceremonies with their partners - the Church's Scripture, tradition and reason become irrelevant to other issues that emerge. The Church is then just a vehicle for the loudest interest group or for culture elites that want a "religious" endorsement of a position.UPDATE: The Anglican Curmudgeon takes on this topic as well, with "Ten Theses" (yes, it harkens to Luther and that is mandatory on a Northern Plains blog). Here's just one (with Curmudgeon's emphasis):
9. As a sacrament of the Church, marriage is not a blessing of the heterosexual lifestyle, but of the union of a man with a woman which reflects the love of Christ, in fulfillment of God's purpose for them.
Mt 19:4 He answered, “Have you not read that from the beginning the Creator made them male and female, 19:5 and said, ‘For this reason a man will leave his father and mother and will be united with his wife, and the two will become one flesh’? 19:6 So they are no longer two, but one flesh. . . .”
And notice how this undoes the "argument from silence." Same sex marriage advocates say, "Jesus never said anything against homosexuality." That's not exactly true, since Jesus affirmed The Law of Moses and the Prophets. But more important than what Jesus might have condemned is what He affirmed, God's design of marriage as male and female.