Pope Pius XII placed the writings of Sister Faustian on the Index of Forbidden Books because he believed what she had written would lead Catholics astray. Her stating that Christ told her she would …More
Pope Pius XII placed the writings of Sister Faustian on the Index of Forbidden Books because he believed what she had written would lead Catholics astray. Her stating that Christ told her she would not need to be judged for example is just wrong. Also she seemed to state Christ told her she was the most perfect creature he'd made.
John XXIII condemned the writings on Divine Mercy, twice. His objection was that there was no evidence of the supernatural origin of these writings and the apparitions are not clearly coming from God. However, the main reason this devotion was considered objectionable was its presenting unconditional mercy.
Further we do have a Feast dedicated to the Sacred Heart which summarizes the whole theology of Redemption, and symbolizes Christ's love and mercy and our need to make reparation for our sins.
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Church Reasons to Condemn the Divine Mercy Devotion by Msgr. Patrick Perez

Several readers have addressed questions to TIA asking orientation about the Divine Mercy devotion. Since we knew Msgr. Perez had addressed the …