The existence of Purgatory is defined as a dogma of the Church by both the Council of Florence and the Council of Trent. Thus it is obligatory for all Catholics who wish to remain in communion with the Church to accept and believe in the existence of Purgatory. The Council of Trent further defined that the souls detained in Purgatory are able to be assisted by the faithful on earth especially by the Holy Sacrifice of the Mass - see Council of Trent Session XXV.
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