The 1999 Joint Declaration on the Doctrine of Justification was certainly an important ecumenical achievement, and I have no difficulty acknowledging that, but I think you are seriously underestimating the depth of the divisions introduced by the Reformation if you believe that an agreement on justification comes anywhere close to resolving them.
In fact, the Declaration itself acknowledges this.
Paragraph 43 explicitly identifies unresolved questions concerning the relationship between Scripture and Church doctrine, ecclesiology, ecclesiastical authority, Church unity, ordained ministry, and the sacraments.
These are not peripheral theological disagreements. They concern the very foundations of Christianity: what the Church is, who possesses the authority to teach in Christ’s name, how apostolic authority is transmitted, and what constitutes the sacramental life of the Church.
Consider the implications.
Catholicism teaches that Christ established a visible, apostolic Church possessing a divinely instituted teaching authority, and that Sacred Scripture must be understood within the apostolic Tradition transmitted and authentically interpreted by that Church.
Much of confessional Protestantism, by contrast, regards Scripture as the sole infallible rule of faith and all of Protestantism rejects the Catholic understanding of the Church’s binding doctrinal authority and the infallibility of ecumenical councils.
How do you reconcile two systems that fundamentally disagree about the very authority by which doctrinal disagreements are supposed to be resolved?
That is not a minor disagreement over biblical interpretation. It concerns the principles governing biblical interpretation itself.
Then consider the sacramental constitution of the Church.
Catholicism maintains that the sacramental priesthood is transmitted through apostolic succession and is intrinsically connected with the Eucharistic sacrifice.
The Lutheran confessional tradition retains an ordained ministry and affirms Christ’s real presence in the Eucharist (although by getting many things wrong about it), but rejects essential aspects of Catholic sacerdotal theology and does not regard uninterrupted sacramental episcopal succession as necessary for valid ministry.
These are competing understandings of what ordained ministry actually is, not simply different administrative arrangements.
And this difference remains so substantial that, in 2007 (eight years after the Joint Declaration)) the Congregation for the Doctrine of the Faith reaffirmed that, according to Catholic doctrine, the ecclesial communities originating from the Reformation lack apostolic succession in the sacrament of Holy Orders and have consequently not preserved the sacramental priesthood and the Eucharistic mystery in their fullness. This assessment is also agreed upon by the apostolic Churches of the east, the Orthodox.
Let that sink in: eight years after the supposed breakthrough of 1999, the Catholic Church was still formally affirming that fundamental elements of the Church’s sacramental constitution had not been preserved in the communities originating from the Reformation.
And the problem extends considerably beyond Lutheranism.
Protestant Christianity encompasses numerous traditions with substantially different understandings of ecclesiastical authority, baptism, the Eucharist, ordained ministry, sacramental theology, and even the relationship between the visible Church and the universal body of believers.
We are therefore not dealing with a single disagreement that can be resolved by finding an acceptable theological formula: we are dealing with deeply entrenched differences concerning the very structure of Christian faith and ecclesial life.
And here is what makes reconciliation extraordinarily difficult: the Catholic Church cannot simply abandon doctrines she holds to have been entrusted to her by Christ and the Apostles without contradicting her own understanding of her identity and authority.
Likewise, Protestant communities cannot simply accept the Catholic understanding of apostolic Tradition, ecclesiastical authority, sacramental priesthood, and the Church’s constitution without fundamentally reconsidering some of the theological principles that historically distinguish them from Catholicism.
In other words, genuine reconciliation would require far more than mutual goodwill, improved relations, or agreement on selected doctrinal questions. It would require a profound convergence concerning the very principles upon which these ecclesial traditions are built.
Compare this with the division between Catholicism and Eastern Orthodoxy.
The differences between East and West are still present , but both traditions preserve a fundamentally sacramental understanding of the Church, apostolic succession, the Eucharistic sacrifice, and a priesthood transmitted through ordination.
That substantial common inheritance provides a foundation for reconciliation (which is also why Patriarch Bartolomew said he expects full communion to be restored ) that is much less complete in the case of many communities originating from the Reformation.
This is the reason why I believe that repairing the divisions created by the sixteenth-century Reformation would require an extraordinary intervention of God.