He means that marriage is mentioned in the bible. (The Word) It is also defined in the bible as well. The definition does not include the joining of two men or two women. A Christian can never accept marriage between homosexuals. It is not possible because Christian marriage is a spiritual joining of the two into the one, one male and one female.
If the secular government wants to create a legal entity, a vehicle to grant secular legal rights to homosexuals, homosexual partners or groups of same, the government certainly may do that, because the government can. Because it can, doesn't make it right. But, again, it can. Christians defer to the authority of government because they are counseled to do so in The Word. But also Christians test the spirit because not all spirits are of God. All things work for good for those who love the Lord and are called according to His purpose. Christians are also counseled to put on the whole armor of Christ. Further if He is for us who can be against us. Further that He is stronger than he that is in the world. Being a Christian is not an opinion. Being a Christian is repentance of sins and accepting Jesus as Savior. It is a living in the spirit while trapped in the flesh. Now we only see things as through a glass darkly, then we shall see things as they truly are.
I have many homosexual acquaintances, some pretty good friends. I do not reject them, nor do I judge them as the complete scripture goes on to say that If I do, I'll be judged in the same way. So, the scripture teaches me not to not judge, but to be very careful in my judgment as I'll be looked at in the same way. As a sinful man myself, I wouldn't stand that scrutiny very well. If I would say to one of my homosexual friends that I would pray for them, I would in the same breath ask them to pray for me as well.
My position is that as American citizens we all must be treated equally under the law. The government doesn't seem to do this very well, even though it is required to do so. The question to me revolves more around the government's failure to, or that it actually create laws that treat equals as not equal. I object to that and we as citizens should speak up in that regard. Now the way that equality comes down, might not necessarily come down the same way. But it should. Marriage as a Christian entity needs to be accepted by government, but perhaps the contractual givens granted marriage should not be. There should be tax policy and contracts that everyone needs to adhere to in order to gain or be a vehicle to gain certain secular legal (not human) rights.