Funny bit of trivia here... when Jesus said what he did about marriage being one man and one woman, he was explaining why divorce is wrong (Mark 10:2-10). Now divorce is commonplace, and they apply the verse to gay marriage instead. So who is it who's really trying to change the definition of marriage?
You make no sense. Yes he was speaking on marriage and divorce. Take another look at the verses
1 Jesus had now finished what he wanted to say, and he left
Galilee and came into the territory of Judaea on the far side of the Jordan.
2 Large crowds followed him and he healed them there.
3 Some
Pharisees approached him, and to put him to the test they said, 'Is it against the
Law for a
man to divorce his wife on any pretext whatever?'
4 He answered, 'Have you not read that the Creator from the beginning made them male and female
5 and that he said: This is why a
man leaves his father and mother and becomes attached to his wife, and the two become one flesh?
6 They are no longer two, therefore, but one flesh. So then, what
God has united, human beings must not divide.'
Right here he not only
defines marriage but answers the Pharisees question. Marriage is sacred because a
Man leaves his father and mother to become one flesh with
his wife
7 They said to him, 'Then why did
Moses command that a writ of dismissal should be given in cases of divorce?'
8 He said to them, 'It was because you were so hard-hearted, that
Moses allowed you to divorce your wives, but it was not like this from the beginning.
9 Now I say this to you: anyone who divorces his wife -- I am not speaking of an illicit marriage -- and marries another, is guilty of adultery.'
10 The disciples said to him, 'If that is how things are between husband and wife, it is advisable not to marry.'
11 But he replied, 'It is not everyone who can accept what I have said, but only those to whom it is granted.
12 There are eunuchs born so from their mother's womb, there are eunuchs made so by human agency and there are eunuchs who have made themselves so for the sake of the kingdom of Heaven. Let anyone accept this who can.'
And right here Jesus comments on how some are to be married and some are not to be married. Divorce is still wrong, just as "homosexual marriage". Why? Because Man and Women are to be joined into one flesh. They shouldn't be separated, and it can not be man and man or women and women.