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Having the one true Faith has little to do with intelligence and everything to do with grace.
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Some of the greatest saints have been rather challenged in ability to learn or compete with their peers.
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St. Thomas Aquinas was known as
"the Dumb Ox."..
St. Joseph of Cupertino was terrified of the examination he would be given wherein he would have to recite a portion of Scripture by memory, in Latin. They had a selection of about 10 excerpts from the Bible to choose from and the best any seminarian could do was to memorize all 10. But Joseph was unable to make any progress on 9 of them, and try as he may, he could only retain one of the 10. Then when he went to his examination, the panel of examiners told him to recite that very one, the one he had learned. He was so happy he spoke with zeal and joy, which made the judges try to make him stop!
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St. John Vianney had a similar experience, whereby he had so much trouble learning the required curriculum he was terrified of being expelled, but he managed to make it all right. Then he was stationed in Ars, which was a small village of party-revelers and pub hoppers. Over the course of a few years gradually all the pubs had to close because the customers stopped coming, for they were spending their time in the Church or at home praying, instead.
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