Around 400 years ago, Christianity was to break apart over the answer. Luther's answer to the question of salvation came down to the alternatives: through grace alone ("sola gratia") or through works such as good deeds, prayer and fasting. This so-called works righteousness became a catchphrase for him against the Catholic Church. The break in this theological question remained and became a marker of the Reformation.
It was not until the ecumenical dialogue of the 20th century that new paths of theological thought were paved towards each other.
A consensus on this controversial issue was also reached 25 years ago, on 31 October 1999, when Lutherans and Catholics signed the "Joint Declaration on the Doctrine of Justification" in Augsburg.
Participating in God's act of redemption
The consensus document stated for both sides: "Justification is by grace alone". It was thus unanimously declared that man cannot rely on his own efforts towards God in any way, but is always dependent on the saving grace of God. Catholics also emphasise man's participation in his justification: 'God does not sanctify man without man'.
The ecumenist Wolfgang Thönissen recalls that it was one of the most controversial questions: "the question of the good works of the justified". Here too, it was agreed that good works follow justification and are the fruits of justification.
However, this consensus ecumenism was not uncontroversial. This is because the declaration was a bilateral document between the Catholic Church and the Lutheran World Federation (LWF).
However, the Evangelical Church in Germany (EKD) also consists of Reformed and United Christians.
But after the Methodists and Anglicans, the Reformed Church also joined the declaration in 2017.
It was hoped that the commemoration of the Reformation in the same year as Martin Luther's theses on 31 October would become a common "celebration of Christ" for Protestants.
In this respect, the Joint Declaration also opened up new paths in multilateral ecumenism. Verena Hammes, Managing Director of the Association of Christian Churches (ACK), sees this as an "ecumenical reception success that cannot be praised highly enough".
Nevertheless, concrete steps resulting from the signing of the declaration have so far largely failed to materialise.
The 2017 commemoration of the Reformation also marked a turning point in the dialogue. In preparation for the great celebration ("Luther Decade"), the EKD published a basic text in 2014 entitled "Justification and Freedom" - but without mentioning the Joint Declaration.
Bishop Bertram Meier, member of the Vatican authority for ecumenism, recognises in such developments that "ecumenism is not static". It is a path on which there are phases of particular intensity, in which one can rejoice at the achievement of milestones, but on which there are also times when it can become steep and arduous and where particular perseverance is required, according to the Bishop of Augsburg.
The next step should now be a declaration on the topics of church, Eucharist and ministry - if possible by 2030, the 500th anniversary of the Augsburg Confession. This summarised the doctrine and practice of the Lutheran Church in 1530.
The Bishop of Augsburg has high hopes for this anniversary. For him, the "Confessio Augustana" is a "pre-confessional testimony of unity". "The Confessio Augustana is such a profound text in theological terms that we should endeavour to treasure it ecumenically," the ecumenist continued.
Unity, not unity
The head of the Vatican's ecumenical authority, Cardinal Kurt Koch, is also currently trying to convince the ecumenical dialogue partners to make a further declaration. However, the Lutheran dialogue partners are finding this difficult.
The leading Lutheran bishop in Germany, Bishop Ralf Meister of Hanover, understands the ecumenical model for Protestantism and beyond as "unity in reconciled diversity".
Ecumenism means "for us first and foremost unity and not oneness", said Meister.
25 years after the Joint Declaration, some hopes for early church unity and Eucharistic communion have not been fulfilled.
Nevertheless, Christians have come closer together. Catholic theologian Verena Hammes therefore hopes that further thought will be given to the liberating message of the doctrine of justification in all its different denominational emphases.
For the ACK, the Joint Declaration is in any case a mandate and obligation for all churches: "Its significance for the togetherness and witness of the churches must and can be explored anew."