The Roman Catholic Church has never doubted what Jesus said as he celebrated the Last Supper with his Apostles. However, familiarity with the words of consecration may have blunted our realisation of what their impact must have been at first hearing. "This is my body . . . This is my blood . . . Do this in remembrance of me". What could this mean?

In his book The Mass (Lit. Press, Minn, 1976), Karl Jungmann points out that the language used by Jesus is ritualistic, cultic and based on Jewish sacrificial rites. It would have been perfectly clear to his hearers that this was no mere suggestion that they should get together occasionally to "remember" him. It was certainly something far more solemn, significant and mysterious.

By the middle ages the "sacred mysteries" used to commemorate the Last Supper had come to be celebrated in a variety of ways; East and West each developing their own characteristic liturgies (i.e., the form of public worship). With these differences the inevitable happened. There were controversies and even wars about them. Superstition and worse sometimes replaced wholesome theology and practice. Instead of trying to conceal the Christian mysteries the liturgy itself became a mystery in need of an explanation!

Then, in 1517, Martin Luther posted his 95 protesting theses, possibly on the church doors in Wittenburg, so introducing Protestantism to Germany and subsequently to the world. Among the many items of Catholic doctrine about which Luther complained was the belief that, in the sacrament of the Eucharist, the bread and wine are changed into the actual presence of the body and blood of Christ. Protestants took the view that the bread and wine used in the sacrament of the Lord's Supper are merely symbolic of what happened at the Last Supper - but no more than that. Some non-Anglican Protestants do not accept the "Real Presence" as understood by Roman Catholics, and although later cosmologies invite further study, cosmological advance does not diminish the mystery of the sacrament.

The Roman Catholic Church, in 1533, promulgated the doctrine of what is called "transubstantiation", defined in the Oxford English Dictionary as meaning "the changing of one substance into another". It is a neologism, i.e., the coining or using of a new word, and was based on the Aristotelian theory that everything which exists consists of matter and form; inner essence and outer appearance.

In 1545, the Council of Trent was set up by the Roman Catholic Church to counteract the doctrines of Martin Luther. During its 18 years of sessions, the general policy, principles and dogmas of the church were authoritatively settled and promulgated. Included in the list was the doctrine of transubstantiation as already announced. The core of that doctrine remains unchanged to this day.

Over 400 years later, the Constitution on the Sacred Liturgy of Vatican II stressed the place of the Eucharist at the very centre of the Christian life, being "a memorial of Christ's death and resurrection, a sacrament of love, a sign of unity, a bond of charity, a Paschal banquet in which Christ is eaten, the mind filled with grace, and a pledge of future glory is given to us".

No organisation can survive without rules, regulations and laws. In the case of the Roman Catholic Church, it is claimed that its laws are based on sound theology. Without sound theology there can, arguably, be no valid Canon Law. The church, as a society, has the right and, indeed, the duty to enact those laws which will ensure the proper and fruitful living of the life of the community and the individual within it. In the case of the Eucharist, these laws govern who may celebrate, officiate at, and receive the sacrament.

Fundamental differences of opinion about these matters are difficult to reconcile. Yet, there has been notable progress. For example, in 1981 the Anglican-Roman Catholic International Commission (ARCIC), under the chairmanship of the then Anglican Archbishop of Dublin, Henry MacAdoo, stated that it had reached what it called "substantial agreement" on its understanding of the Eucharist.

The Vatican responded by asking for clarification from ARCIC on its understanding of (among other things): (i) Christ's "Real Presence" in the Eucharist and (ii) attitudes towards the reservation of the sacrament. Subsequently statements by the (Roman) Pontifical Council for Christian Unity and the (Anglican) Lambeth Conference confirm that, in their view, there no longer exists any doctrinal barrier to unity. Meantime, the theologians and the lawyers work on.

In matters of sharing Communion there have been tentative advances. Pope John Paul II, in his encyclical Ut Unum Sint (That they may be One), says: "It is a source of joy to note that Catholic ministers are able, in certain particular cases, to administer the sacraments of the Eucharist, Penance and Anointing of the Sick to Christians who are not in full communion with the Catholic Church, but who greatly desire to receive the sacraments, freely request them, and manifest the faith which the Catholic Church professes with regard to these sacraments."

Conversely, in specific cases and in particular circumstances, Catholics too can request these same sacraments from ministers of churches in which these sacraments are valid. (The admission, even by implication, that there are "valid" sacraments in such churches is a significant step forward.)

The question of the recognition, or otherwise, of Anglican ordination by the Roman Catholic Church remains thorny, particularly since the unilateral Anglican decision to ordain women.

However, some theologians take at least a fragment of hope from the wording of the ceremony of ordination of those Anglican clergy who have become Catholic priests, when it speaks of ". . . the value . . . the fruitfulness for salvation of (their) faithful ministry in the Church of England."

And it is known that the present Holy Father gave communion, at a private Mass in the Vatican, to the late Rev Sheila Brown, who had only shortly before been ordained an Anglican priest and who, at that Mass, wore her "Roman" collar.

And, all the while, if not always apparently centre-stage, there is the Holy Spirit, the Spirit who guides and directs the church, keeping her free from serious error and sanctifying her members. In the Spirit lies our hope that Christ's prayer "that they may all be one" will not be frustrated forever. In the Spirit lay the hope of the Apostles, the Church Fathers and Christian folk of all ages. So may it be with us.

Where does all this leave us? It can be argued that a belief in God, a belief in Jesus Christ, transcend belief or unbelief in the dogma of the Real Presence. And that, surely, is enough to encourage all Christians to follow the example of Christ himself, and go forth in love, compassion and hope towards full reconciliation and unity. All Christians should be guided, sustained and united by the things we hold in common, while respecting each other in those things where we differ.

Billy FitzGerald is a former member of the international Societas Liturgica, which reviews the theology and discipline of the Eucharist. He is also a former head of religious programmes at RTE.