To have Mass offered for the Holy Souls is the most efficacious relief

To have Mass offered for the Holy Souls is certainly the most efficacious way of relieving them.

"Since it is certain by the doctrine of the Catholic Church, that the souls detained in purgatory are benefited by the prayers of the faithful, and especially by the august Sacrifice of the Altar, we think we can give them no more useful and desirable pledge of our love than by everywhere increasing the offering of the pure oblation of the Most Holy Sacrifice of Our Divine Mediator, for the extinction of their pain."

Pope Leo XIII, encyclical Quod Anniversarius, 1888

Thank you Sue