There has been a lot of Christian articles recently on the whole "gay marriage" issue and after reading a fair number of them (both for and against) they all seem to have the same issue - they are working with an incorrect definition of marriage and as a result draw erroneous conclusions.
Genesis 1 and 2 are normally taken as the bedrock of where marriage is defined. At this time the world was perfect so there was no need for either party to be protected from anything as sin had not yet entered the world. And so in Genesis 2:24 we read:
For this reason a man will leave his father and mother and be united to his wife, and they will become one flesh (Genesis 2:24 NIV)
And that's what marriage is. There are a lot of things we have added to it but at it's core that's it. The church has implicitly assumed this through the ages, even if not explicitly, as they recognised that an unconsummated marriage could be declared null en void because the marriage had never taken place. It also means you don't have to be a Christian to get married. Any male and female that engage in sex get married. As Christians we implicitly recognise this in not forcing people who were not married in a church to get "(re)married" if they become Christians. We recognise that the church part of it is completely irrelevant.
Does the rest of Scripture support that definition? Paul writes this in 1 Corinthians 6:16:
Do you not know that he who unites himself with a prostitute is one with her in body? For it is said, "The two will become one flesh." (1 Corinthians 6:16 NIV)
So you have married as many people of the opposite sex you have had sex with. This also turns the whole no sex before marriage thing on its head. Jesus makes this even clearer. In Matthew 19:4 he says:
"Haven't you read," he replied, "that at the beginning the Creator 'made them male and female', and said, 'For this reason a man will leave his father and his mother and be united to his wife, and the two will become one flesh'? So they are no longer two, but one. Therefore what God has joined together, let man not separate." (Matthew 19:4-6 NIV)
So if we use the sexual union of male and female as the definition of marriage (which I believe is the only definition of marriage found in the Scriptures) then the whole issue of "gay marriage" becomes a non-issue, not because of anything the church says or anything the state says but because, very simply, it is physically impossible for them to get married.
So what about church "marriage"? If we use the above definition then the church does not marry anyone - in fact it can't. What the church does is provide a platform where the couple can exchange vows before God and witnesses. This has a two fold purpose. One is that the couple are making vows before God that they will stay together for the rest of their lives. This makes divorce among Christian couples far more serious than among non-Christian couples who have not made any vows to God. A secondly it provides witnesses who hear them make the vows and can keep them accountable to those vows. It's interesting that the Puritans didn't believe the church should be involved in "marrying" people - they considered it purely a state issue.
And what about state "marriage"? Again, using the above definition of marriage the state does not marry anyone. What it does however is provide legal protection for two or more parties. Essentially, the state provides a cohabitation contract, which can be between a male and female, two males, two females or any other combination of people. The only requirement is that all the parties be of legal age. France went down this route and I believe this is the correct way for the state to handle this issue. Whether or not the two or more parties are having sex or not is completely irrelevant in terms of the contract. And it is right that the state does this as it is the state's role to protect it's citizens, both from external harm as well as internal harm. So technically the state legislation should have no reference to the term "marriage" in it at all. It's irrelevant and confuses the issue.
So should gays be able to be "married"? If you mean by that should they be able to enter into the same legal contracts that "married couples" do then yes. If you mean should they be able to get "married" in a church then no. But then even a man and woman can't get "married" in a church either.
There is a lot more I could write about this topic (e.g. adoption of children and "marriage") but that's probably enough for now. Maybe I'll pick up the pen another day and write some more.