We cannot be 100-percent certain without asking Pier Giorgio directly. However, one saint in particular seems to have held the greatest influence: the apostle St. Paul.
Pier Giorgio often made references to St. Paul in letters to his friends. For example, on January 15, 1925, he wrote to Marco: "There is a lack of Peace in the world which has distanced itself from God, but there is also a lack of Charity; that is, true and perfect Love. Maybe if all of us listened more to St. Paul, human miseries would be slightly diminished."
After losing a bet with his friend Laura Hidalgo, he gave her a copy of the Epistles of St. Paul in Latin. Later, he gave her the Italian translation. He discussed this gift in a letter to Marco on April 24, 1925: "The other day I finally paid my debt to Laura. I brought her the (copy of) St. Paul in Latin which pleased her very much, now I’ll send her the Italian translation of the epistles because as I explained to her I want her to read them and it’s difficult to understand St. Paul in Latin, but having the Latin Text and the translation one can comprehend the beauty of such epistles."
On April 29, 1925, just two months before his death, Pier Giorgio wrote to his friend Isidoro Bonini encouraging him to read the writings of St. Paul: "...the mind every now and then finds peace and relief and spiritual enjoyment in reading Saint Paul. I’d like you to try and read St. Paul: he is marvellous and the soul is uplifted by this reading and we are prodded to follow the right way and to return to it as soon as we leave it through sin."
Certainly, Pier Giorgio admired many saints. However, the impact of St. Paul and his Hymn to Charity are profoundly evident in the life of charity by which Pier Giorgio lived and died.