Pope says it's a 'grave sin' to deny God has blessed other Christians

Just as divisions in society grow when wealth is not shared, divisions within Christianity grow when the richness of gifts God has given to one Christian church or community are not recognised and shared, Pope Francis said.

"It is easy to forget the fundamental equality existing among us: that once we were all slaves to sin, that the Lord saved us in baptism and called us his children," the Pope said during an ecumenical vespers service at Rome's Basilica of St Paul Outside the Walls.

At the beginning of the service, Pope Francis, Orthodox Metropolitan Gennadios of Italy and Malta and the Rev Tim Macquiban, minister of Rome's Ponte Sant'Angelo Methodist Church, paused for a moment of prayer before the tomb of St Paul.