Pope Francis has celebrated a final mass to close out a historic meeting of bishops that, by a single vote, approved an important new direction in welcoming divorced and civilly remarried Catholics into the church.

In his homily in St Peter's Basilica, Francis declared: "Today is a time of mercy."

Without changing church doctrine, the 275 synod "fathers" on Saturday approved a 94-point final document endorsing Francis's call for a more merciful and less judgmental church.

The most disputed section of the document concerned whether remarried Catholics can receive Communion.

While the document does not chart any specific path to receiving the sacraments as originally sought by liberal prelates, it opens the door to case-by-case exceptions by citing the role of discernment and individual conscience in spiritual direction.

With the badly divided church hierarchy before him, Francis took veiled aim at those in the church who place more importance on doctrine and law than on God's mercy and forgiveness.

He warned them of the risk of "becoming habitually unmoved by grace," of turning a cold shoulder to God's most wounded children and of a "spiritual illusion" that doesn't let them see the reality of their flock before them and respond to it.

"We are capable of developing views of the world, but we do not accept what the Lord places before our eyes," he said. "A faith that does not know how to root itself in the life of people remains arid and, rather than oases, creates other deserts."

The key paragraph in the report - which says a case-by-case approach is necessary when dealing with remarriage since not everyone bears the same responsibility for the preceding divorce - passed with only one vote more than the two-thirds majority necessary.

Its passage will give Francis the room to manoeuvre that he needs if he wants to push the issue further in a future document of his own.

German Cardinal Reinhard Marx, who spearheaded the German theological initiative that was decisive to getting the majority, said he hoped that Francis would issue it during his upcoming Jubilee Year of Mercy, which starts on December 8.