God designed marriage and the family as a reflection of the Most Holy Trinity and the Holy Family. Advocating for marriage to be something other than one man, one woman, for life is to advocate for a new sort of iconoclasm. Ultimately, it destroys the historical Christian icon of the family replaces it with something new. This:
I found the second image by going to Google Images and searching for “gay nativity.” There are so many things wrong with that image, and I hope to blog about those details another time. But just to whet your appetite: the theological implications of two Christs (or three, if we include the original configuration); using marriage to segregate the sexes; the abolition of sexual sin; the enshrinement of sexual sin; undermining the divinity of Christ; the abolition of sex differences; the abolition of Mary, Mother of God; the child as chattel and the object of a contract.
Marriage is only between one man and one woman. As part of the ordinary and universal Magisterium of the Church, this teaching is dogmatic and infallible. It cannot change, ever. Not only that, but to teach otherwise is to lead little ones astray and to cause them to stumble.
I am passing along to you that which was handed to me. Christians who advocate for “marriage equality” are not doing that. They have made up a new teaching and are trying to get support for it by saying that it is consistent with larger themes of the Church such as mercy, charity (love), and justice. They distort those concepts and so are gravely mistaken. Do not listen to any of them and do not be frightened by predictions that the Church will change her teaching on this point. She will not. The true teaching will prevail. Praise God for that.