Former US president Jimmy Carter is in the biggest fight of his life as he battles cancer, which his doctors said had already spread to his brain, but the 90-year-old Baptist and church deacon is not letting even this gravest of sickness to stop him from sharing his faith in God to other people.

Speaking before the Maranatha Baptist Church in Plains, Georgia, on Sunday, Carter touched on the theme of love and called it "the most important aspect of Christianity," News Max reported.

Carter said he and his wife of 69 years, Rosalynn, show their love for each other by resolving never to go to sleep without settling their arguments and differences. "Just being able to admit you might be mistaken and that the other person might be right" will improve any relationship, Carter said, much to the delight of the huge crowd that attended his Sunday school.

He also encouraged the packed congregation to consider God as a partner in their lives.

"Any time, we can just bow our heads and say, 'God, I'm really troubled. I ask you to give me the strength to bear whatever is on my shoulders and to bear whatever comes to me,'" Carter said.

The dedicated Christian has been teaching Sunday school for over three decades already, and his small red-brick church draws in a regular attendance of 40 members. However, after his recent admission of cancer, the crowd ballooned up to 460 people.

Because of the overwhelming turnout, Carter even gave a second lesson at a nearby high school for around 250 people, although he was forced to turn away 70 other listeners.

Some of those who were lucky enough to get a seat for Carter's sermon said they felt "blessed" just to hear his words. Chet and Stephanie Cranfield of Merritt Island, Florida, told Yahoo! that they were comforted by Carter's message of optimism, and have renewed their faith in God now that Chet would be taking chemotherapy in November for kidney cancer.

"He was wonderful. I feel uplifted," Chet said, while his wife of 32 years added: "Like God can carry you through anything."