Some people consider Billy Graham, 98, as the most influential living Christian today. He is known for his crusades, which have brought hundreds of thousands of people to Jesus Christ. He has also made a name for himself as spiritual adviser to a number of U.S. presidents.

But when a letter writer asked Graham who he thought was the greatest Christian who ever lived, the evangelist did not name himself. Instead, he said this Christian might have lived a life away from the limelight, quietly carrying out God's instructions.

"Only God knows our hearts and minds, and only He knows who has followed Christ most faithfully across the ages," he wrote on his website. "I suspect, however, that it probably would be someone you and I have never heard of —someone who humbly lived for Christ in very difficult and obscure circumstances, but loved Christ and lived for Him regardless of the cost."

Graham shared two truths that people need to consider. First, he said even the most faithful Christian is not perfect, so others "shouldn't slavishly follow their example." People can learn from them and be thankful for them, but they should not be the ultimate model on how to live one's life.

The next truth, according to Graham, is that only Christ is worthy to be that model. "He was God in human flesh — and as such, He alone was perfect and without sin. His love was perfect; His purity was perfect; His obedience to His Heavenly Father was perfect. And because He was perfect, He alone was able to take upon Himself your sins and mine, and give His life as the final sacrifice for our salvation," he said.

After accepting Christ, believers have to embrace the life of responsible discipleship, Graham said. Nowadays, people want Christ without responsibility, but Graham said there's no such thing.

"Whatever work a Christian does is done unto the Lord," he said. "He should do his best at whatever his trade or vocation. He should be faithful, clean, and honest."