Protestant and Catholic leaders are gathering in Chicago on Thursday to mark the tenth anniversary of a landmark ecumenical agreement made between the two faith traditions.

Considered the most significant agreement since the Reformation, the Joint Declaration on the Doctrine of Justification was signed by the Vatican and the Lutheran World Federation on Oct. 31, 1999 in an effort to end centuries of doctrinal dispute.

"For hundreds of years, the issue of justification by faith divided Catholics and Protestants," said Bishop Gregory Palmer, president of The United Methodist Church’s Council of Bishops, in a released statement. "This agreement celebrates consensus on the basic truths of the doctrine of justification."

Methodists joined the agreement in 2006 during a World Methodist Council meeting in Seoul, South Korea.

Representatives from all three traditions will be celebrating at Old St. Patrick's Church in Chicago while a second celebration is scheduled to take place on the actual anniversary date in Germany, where the joint declaration was signed.

"The JDDJ is a powerful testimony to what can be achieved when churches remain in dialogue addressing questions that have separated us for centuries," said LWF president the Rev. Mark S. Hanson, who also serves as presiding bishop of the Evangelical Lutheran Church in America.

The doctrine of justification was at the center of the sixteenth century Reformation. As the LDDJ states, "justification was the crux of all the disputes" between the Roman Catholic Church and the Lutheran tradition. Thus, the two faith groups believed that a common understanding of justification was "fundamental and indispensable" to overcoming the division.

Justification, according to the document, is the forgiveness of sins, liberation the dominating power of sin and death, and from the curse of the law, and it is acceptance into communion with God – all of which is from God alone, for Christ's sake, by grace, through faith in the gospel of God's Son.

In their common understanding, the Lutheran churches and the Roman Catholic Church together confess: "By grace alone, in faith in Christ's saving work and not because of any merit on our part, we are accepted by God and receive the Holy Spirit, who renews our hearts while equipping and calling us to good works."

The joint declaration does not cover everything that either church teaches about justification but it encompasses a consensus on basic truths of the Christian doctrine.

Still, differences remain over language, theological elaboration, and emphasis in the understanding of justification with regard to such matters as good works but the Lutheran and Catholic churches say those differences do not destroy the consensus regarding the basic truths.

The JDDJ was not signed without objections. Some in the Lutheran tradition were shocked to see their leaders make what they described as a compromising move.

Robert Preus, author of Justification and Rome, said the agreement compromises Lutherans' witness to the evangelical Lutheran doctrine on justification and the confessional principle itself.

Nevertheless, the joint declaration is often cited as a significant achievement in religious history, the Rev. Donald J. McCoid, executive, ELCA Ecumenical and Inter-Religious Relations, told the ELCA News Service.

The Chicago gathering is being attended by Hanson; LWF General Secretary the Rev. Ishmael Noko; Cardinal Francis George, who leads the Roman Catholic Archdiocese of Chicago and is president of the U.S. Conference of Catholic Bishops; and Palmer, among others.