The Pope has confessed that he gets "annoyed" when people quote what Jesus said to the woman caught in adultery: "Go and sin no more."

Instead, he said, priests must show mercy. They must allow themselves to be "moved" by the weaknesses, sins and sufferings of their parishioners.

In a meditation preached at St Paul's Outside the Walls in Rome for the Jubilee of Priests, Pope Francis spoke about Jesus' encounter with the woman caught in adultery recorded in John 8.

Referring also to the plight of refugees attempting to cross oceans to safer lands, he urged priests to embrace mercy. "We can ask for the grace to taste with the crucified Jesus the bitter gall of all those who share in his cross, and smell the stench of misery – in field hospitals, in trains and in boats crammed with people."

He admitted the Church has always had its own sins and failings.

"But when it comes to serving the poor by the works of mercy, as a Church we have always followed the promptings of the spirit."

He also said he had always been struck by the passage of Jesus' encounter with the adulterous woman, and his refusal to condemn her.

Pope Francis said: "In response to the question they asked to test him – 'should she be stoned or not?' – he did not rule, he did not apply the law. He played dumb, and then turned to something else. He thus initiated a process in the heart of the woman who needed to hear those words: 'Neither do I condemn you.' He stretched out his hand and helped her to her feet, letting her see a gentle gaze that changed her heart."

The Pope then continued: "Sometimes I feel a little saddened and annoyed when people go straight to the last words Jesus speaks to her: 'Go and sin no more.'

"They use these words to 'defend' Jesus from bypassing the law. I believe that Christ's words are of a piece with his actions. He bends down to write on the ground as a prelude to what he is about to say to those who want to stone the woman, and he does so again before talking to her."

Jesus was in fact opening a space of "non-condemnation", the Pope said.

His command, "Go and sin no more", had to do with the future, to help her to make a new start and to "walk in love", he added. "Such is the sensitivity of mercy: it looks with compassion on the past and offers encouragement for the future."

He said the "no" has to be said to the deeply-rooted sin present in everyone.

"In that woman, it was a social sin; people approached her either to sleep with her or to throw stones at her. That is why the Lord does not only clear the path before her, but sets her on her way, so that she can stop being the 'object' of other people's gaze and instead take control of her life.

"Those words, 'sin no more' refer not only to morality, but, I believe, to a kind of sin that keeps her from living her life."