Is this true? What is the nature of this "redefinition"?
I think we gain an important insight into this from an interesting story that has just emerged from Australia. The Anglican Diocese of Sydney has added the word "submit" to the vows a wife makes to her husband in the marriage ceremony. In the proposed new wording the minister will ask the woman "Will you honour and submit to him, as the church submits to Christ?'
This is justified by the very conservative bishop by explicitly saying that equality between sexes is wrong. Clearly women need to submit to men, according to this bishop.
This is the argument for "traditional" marriage. It is about one woman (or more) submitting to a man. It's about women becoming, in some sense, the property of men.
In this understanding of marriage obviously same sex marriage makes no sense, because there can be no submission. In same sex marriage there cannot be a power differences between sexes, so there cannot be "traditional" marriage.
So when people talk about the "redefinition" of marriage I say, yes, we are talking about a redefinition, but for most of us, this redefinition has already happened. The redefinition is about understanding marriage as a partnership between equals. The redefinition happens when we consider women equal to men.
So the redefinition happens when we consider marriage a partnership of equals.
If you understand marriage as being a partnership between equals, then same sex marriage makes sense. Two men and two women can be just as much a partnership of equals as a woman and a man.
But if you consider marriage to be about men having authority over women, then same sex marriage will never make sense, because there can be no power differential between the two people based on sex.
This is why I believe same sex marriage as the potential to redeem and renew marriage, by confirming it as a partnership of equals, by purging it of its sexist undertones for everyone.
I once heard someone, I think it was Gene Robinson, say these words, and I believe they really apply here:
"Homophobia is just one small room in the mansion of sexism."