The Vatican announced this week that Benedict XVI plans to allow Anglican communities to enter into full union with the Catholic Church while preserving elements of their distinctive spiritual and liturgical heritage. This has taken many people by surprise but it is very good news.

Hopes of reunion between Anglicans and Catholics go back a long way. Through the 19th century Oxford Movement esteem for the Catholic Church grew among Anglicans and some "crossed the Tiber". Cardinal John Henry Newman, soon to be beatified by the Pope, is the best known example.

But again and again corporate reunion found obstacles in its way. In each generation Anglicans wishing for full union with the Church of Rome found themselves having to make the journey alone. However, in so doing, they have helped to clarify what is at stake.

In 1896, union foundered on the decision by Pope Leo XIII that Anglican Orders were invalid. In other words, in the eyes of the Catholic Church, Anglican priests and bishops did not have the powers of true priests and bishops because they had lost the link of succession to Christ's Apostles. To many Anglicans this proved a deep disappointment. I think it was the famous writer and translator Ronald Knox who said, after he became a Catholic priest, that at least he had been making many spiritual communions when he celebrated the Anglican Eucharist.

But Pope Leo’s decision clarified how essential the apostolic succession is. It is only because they descend directly from the Twelve Apostles who received divine powers from Christ himself that Catholic priests can consecrate the real Body and Blood of Christ in the Mass and forgive sins in Confession.

Then there was contraception in the 1920s. After the Anglican Communion decided to change its teaching at its Lambeth Conference in 1930, Pope Pius XI made it clear that birth control was wrong and the Catholic Church had no power to change that. This teaching was reiterated by Paul VI in 1968, against the views of not a few people who thought that the Church must inevitably bow to current opinion.

Something similar happened with the refusal by the Catholic Church to ordain women to the priesthood. There are now a number of women who have received ordination as priests and bishops in the Anglican communion. Pope John Paul II pointed out that neither he nor the Church has any power to change the teaching of Christ on this matter. The Church is not a fiefdom of the Pope; but neither is it a democracy.

All these developments have caused some Anglicans to reflect more deeply upon the nature of Christian unity and especially the authority of the Pope in preserving the authentic teachings of Jesus Christ throughout the centuries. They have come to believe that these are to be found fully only in communion with the Bishop of Rome.

So, after decades of discussion, study and prayer, Benedict XVI has found a solution. He is to issue an Apostolic Constitution which will create a structure within Catholic canon law called a "personal ordinariate". This will allow former Anglicans to enter full communion with the Catholic Church. This arrangement is good news but it may not have an easy journey.

Anglicanism started in England (where the Anglican Church remains the established church) but it has now spread throughout the English-speaking world, notably to North America, Australasia and English-speaking Africa. "Personal ordinariates" are designed for those Anglicans who really do want to enter into full communion with Rome, but at the same time wish to preserve “elements of the distinctive Anglican spiritual and liturgical patrimony”. In some countries, England being one, there has been considerable hesitation about establishing national Catholic communities, such as Poles or Brazilians. The bishops have much preferred everyone to attend the same liturgy in the same parish on Sundays. This question has been tackled differently in the United States, which means that the establishment there of Episcopalian (as Anglicans are called there) communities would seem to pose fewer difficulties.

Then there is the question of relations with those Anglicans who do not wish to enter into full communion with the Catholic Church: how will this Apostolic Constitution affect them?

On a positive note, recent experience with the entry into the Catholic Church of many Anglican clergymen (not a few of them married) who have then been ordained to the Catholic priesthood has proved to be very favourable. Their fervour and dedication is providing a great service to the Church. But this does pose the question of the continuing role of married clergy in the Catholic Church. Hitherto the arrangements  have been considered exceptional and of a transitory nature. The head of the Congregation for the Doctrine of the Faith, Cardinal William Levada, has already clarified that while married Anglican clergy can be ordained as Catholic priests, there can be no question of married bishops.

Sorting out these complications has been challenging for the Vatican. "We have been trying to meet the requests for full communion that have come to us from Anglicans in different parts of the world in recent years in a uniform and equitable way," Cardinal Levada commented. "With this proposal the Church wants to respond to the legitimate aspirations of these Anglican groups for full and visible unity with the Bishop of Rome, successor of St Peter."

This Apostolic Constitution on behalf of the Anglican Church should perhaps also be seen in the context of the studies which are due to commence next week regarding the return of the members of the Society of St Pius X -- founded by break-away French archbishop Marcel Lefebvre -- into full communion with the Church. Not a few people will hope that gestures of welcome to the Anglicans will also be extended to the members of this society.

The path towards Christian unity is an exciting and difficult one. As the Second Vatican Council taught, the heart of ecumenism lies in conversion: “Conversion of the heart, holiness of life and prayers, in private and in public, for the unity of Christians must be considered the soul of the ecumenical movement”. With prayer and charity nothing is impossible. This is a moment for much prayer, charity and union with the Holy Father’s intentions.

Father Andrew Byrne is a Catholic priest in London