CHICAGO (CBS) – Cardinal Francis George, speaking Sunday at a mass to celebrate the golden anniversaries of more than 400 couples, used the celebration as a platform to reiterate the Catholic Church’s opposition to same-sex marriage.

The cardinal spoke at a ceremony where 400 couples who have been married for 50 years renewed their wedding vows at Holy Name Cathedral.

George honored the couples for their lifetime commitments to each other, and the families they have helped to raise.

“I thank you for the way in which you are open to others in Christ’s name. I think you for the way you raised your children, and now love your grandchildren in his name. This is a marvelous moment, and I thank God for being with you today, as you celebrate it,” he said.

Without mentioning gay marriage specifically, George also spoke briefly about the Catholic Church’s opposition to legalizing same-sex marriage, saying the institution of marriage is something that “comes to us from God,” not from the church or from the government.

Quoting from the Bible, George said marriage has always been a union between one man and one woman, and should not change.

“Marriage is what it is, what Jesus said from the beginning: Two in one flesh, for which man leaves his family and joins himself to his wife; and wife leaves her family, and joins herself to her husband,” he said.

George, leader of the nation’s third largest Catholic Archdiocese, said there must be a way to honor the rights of gays and lesbians, without legalizing same-sex marriages.

In January 2011, Gov. Pat Quinn signed legislation legalizing same-sex civil unions in Illinois. He also has pledged to help the push for same-sex marriage in the state.

George said, “There must surely be ways in our civil society, where we can honor friendships, where we can respect other people, without destroying the nature of marriage. It is very important, for your whole lives, give witness to what marriage truly means. And while civil laws might change – if they do – then society will be the worse for it.”

The cardinal also discussed his recent chemotherapy treatment for his second bout with cancer.

“It’s an odd kind of situation where they fill you with poison for a while then they let you rest for a while. So this is the resting period. The reason they let you rest is because your immune system is so weakened that you’re not supposed to be around people until the white blood cell or whatever goes up,” he said. “So I was told not to be around crowds. So this is not a crowd … this is a group of fine disciples of the Lord, whom we worship together this afternoon. It’s a great pleasure for me and I thank you.”

Doctors discovered cancerous cells in George’s kidneys this summer, and he has been undergoing chemotherapy. He also was diagnosed with bladder cancer in 2006 and underwent surgery in August of that year.