Even though there are some Catholic groups that have agreed that same-sex marriage should be recognised as a sacrament, a professor of moral theology from the Catholic University of America is saying that this cannot happen because marriage is created by God, and not even the Church has a right to change that.

In response to groups such as Dignity USA calling out for "sacramental equality," Dr. John Grabowski said people should not be demanding things like this especially when they have "a lack of understanding of what the Church is and the nature of the Church and what the sacraments are."

"'Marriage equality' made for a good slogan, but in the Church's understanding, marriage is not something that can be 'redefined'; if you will, by interest groups, by government, or even by the Church itself," he told CNA.

Dignity USA earlier called for same-sex marriage to be granted "full access to marriage and ordination" in the Catholic Church. They even approved a resolution that called on Catholic leaders to "ensure that all of the sacraments of our Church be administered regardless of the gender identity, sexual orientation, or relational status of the person(s) seeking the sacrament."

Grabowski called Dignity USA's position as "unfortunate" since there is no way for people—or even the Church for that matter—to change or redefine marriage. God's views on marriage can be found in Genesis, he said, when God created male and female and told them to "be fruitful and multiply."

Marriage also reflects God as "a communion of persons" and a "unity of love," added Grabowski, and it shows how couples can "participate in his great capacity to create new life in God's image."

"Unjust discrimination is always morally evil, but not all distinction is discriminatory and unjust," he said.