"Never condemn. If you feel like condemning, condemn yourself, there's got to be something there, huh?" he said, according to Vatican Radio.
In his homily, the pope talked about hypocrites rigidly adhering to rules while letting their weak hearts be swayed by shifting and selfish interests.
Looking at the day's Gospel reading from St. Matthew (21:23-27), the pope said the chief priests and elders who questioned Jesus' authority were hypocrites.
Their outer appearance made them seem "strong," he said, but on the inside, their "hearts are very weak, they didn't know what to believe in and that is why their life was so regulated on the outside," he said.
They focused only on slavishly following rules and rituals, and criticized those who did not.
"They weren't interested in the truth," he said, they vacillated here and there, seeking only their best interests, letting "the wind" decide which way to go, like "weather vanes."
Jesus is the exact opposite: He teaches us that the Christian must have a strong heart, a firm heart, a heart rooted on the rock, who is Christ."
With Christ as the guide, one can move forward, but with prudence, deciding how to act according to each situation, but without compromising the heart, the pope said; "you don't negotiate the rock. The rock is Christ, you do not bargain."
Jesus never compromised his heart as son of the Father, "but he was so open to the people, looking for ways to help," while the elders complained, "Our doctrine says that cannot be done." They insisted "the discipline is untouchable, it is sacred."
Pope Francis compared their attitude to the situation when he was a boy and it was forbidden for anyone to have anything to eat or drink before receiving Communion.
"You couldn't even have a drop of water. Not at all. And you had to make sure you didn't swallow any water when brushing your teeth. I myself as a boy went to confess that I had received Communion even though I thought a drop of water had gone down" that morning.
"Pope Pius XII freed us from that heavy cross of eucharistic fasting," he said.
But when the pope changed the rules, there were people who exclaimed, " 'Ah heresy! No! He touched the discipline of the church.' Many Pharisees were scandalized. Many."
But Pope Pius had done only what Jesus would have, he said. He said Pope Pius saw the people suffering, especially when it was hot, and the priests had to say as many as three Masses all in a row well past noon while fasting.
Pope Francis said that sometimes when he sees a Christian who has a weak heart that is not built on Christ, but they are "so rigid on the outside, I have asked the Lord, 'Lord, throw a banana peel down in front of them so that they'll take a nice fall. By feeling the shame of being a sinner they will encounter you, you who are the savior.'"
He said it is only by recognizing ourselves as sinners and feeling that shame of sin that people open their eyes to God, "who forgives us, like the sick who went to the Lord to be healed."
Carol Glatz; Catholic News Service; National Catholic Reporter; 15 December 2014