Pope Francis has lashed out at "rigid" Catholic idealists who follow a "this or nothing" style of evangelism, calling them "heretical" and "not Catholic."

Speaking during morning Mass on Thursday, the Pope told congregants at the chapel in the Vatican guesthouse that Catholics need to have a "healthy realism" in their approach to their faith, the Religion News Service (RNS) reports, quoting Vatican Radio.

The pontiff said Catholics should try their best to seek reconciliation with people of other faiths rather than follow strict rules.

"Many times you can't reach perfection, but at least do what you can, come to an agreement," Pope Francis said during his homily.

He said the faithful should follow the example set by Jesus who, he said, adopted a "healthy realism" in His teachings.

"This [is the] healthy realism of the Catholic Church: the Church never teaches us 'or this or that.' That is not Catholic. The Church says to us: 'this and that.' 'Strive for perfectionism: reconcile with your brother. Do not insult him. Love him. And if there is a problem, at the very least settle your differences so that war doesn't break out.' This [is] the healthy realism of Catholicism. It is not Catholic [to say] 'or this or nothing:' This is not Catholic, this is heretical," Pope Francis said, according to Vatican Radio.

"Jesus always knows how to walk with us. He gives us the ideal. He accompanies us towards the ideal. He frees us from being caged in by the rigidity of the law and he tells us: 'But, do as much as you can.' And he understands us well. He is our Lord and it's this which he teaches us," the pontiff said.

Commenting on the Pope's remarks, author John-Henry Westen noted that "interpreting what Pope Francis is saying in a precise way has always been difficult."

However, the Pope has been consistent in criticising people who hold on to "rigid" religious beliefs, said Henry Westen, the co-founder and editor-in-chief of LifeSiteNews.

While returning to the Vatican from Africa in November last year, the Pope told journalists that "fundamentalism is a sickness that we find in all religions."

"Among Catholics there are many, not a few, many, who believe to hold the absolute truth. They go ahead by harming others with slander and defamation, and they do great harm... And it must be combated," the Pope said.

However, Henry Westen said an accusation of rigidity or heresy by Pope Francis against those who would insist on the ideal of Christ's teaching such as marriage, "would fall heavily on Francis' own predecessor, Pope St. John Paul II, whom Pope Francis himself declared a saint."

The author said in the encyclical Veritatis Splendor, John Paul taught: "It would be a very serious error to conclude... that the Church's teaching is essentially only an 'ideal' which must then be adapted, proportioned, graduated to the so-called concrete possibilities of man, according to a 'balancing of the goods in question'."

Pope Francis' condemnation of heresy against "this or nothing" Catholics would also run counter to the statements made by Cardinal Robert Sarah, who Pope Francis appointed to head the Congregation for Divine Worship and the Discipline of the Sacraments.

In his book "God or Nothing," Cardinal Sarah strongly rejected the idea of watering down the teaching on the indissolubility of marriage with pastoral leniency. "The idea of putting magisterial teaching in a beautiful display case while separating it from pastoral practice, which then could evolve along with circumstances, fashions, and passions, is a sort of heresy, a dangerous schizophrenic pathology," he wrote.

Cardinal Sarah even warned prelates who would seek to alter doctrine by altering the practice of the Church regarding marriage. "Men who devise and elaborate strategies to kill God, to destroy the centuries-old doctrine and teaching of the Church, will themselves be swallowed up, carried off by their own earthly victory into the eternal fires of Gehenna," he said.