What is Roman Catholic teaching of Treasury of Merits and what it was used for?

Answer 1

The Roman Catholic church has a concept called Indulgences. An indulgence is a remission of the temporal punishment due to sin, the guilt of which has been forgiven.

According to Roman Catholic Church theology, in the early days of the Church, the great saints died and went to heaven before they had used up all their accumulated merits, which are earned by all Catholics while doing good work on Earth. The Church had possession of these extra merits and could, in the Church's teaching, sell them back to the people over time in the form of Indulgences, thus allowing one to buy merits, rather than having to do the good works required to earn them.

Treasure House of Merit (or treasure of merit) was one of the core complaints of Martin Luther at the start of the Reformation in his Ninety-Five Theses. While Luther did not question that the Treasure House of Merit existed, he rejected the belief that the Church had sole possession of it. He believed instead that God had given merits equally to everyone, and thus merits could not be sold by the Church.

Roman Catholic Theology has considerably evolved since Martin Luther's Reformation. Today an indulgence is the extra-sacramental remission of the temporal punishment due, in God's justice, to sin that has been forgiven, which remission is granted by the Church in the exercise of the power of the keys, through the application of the superabundant merits of Christ and of the saints, and for some just and reasonable motive.

For a more complete exposition on Indulgences see the related link.