Despite the religious sentiment behind the letter from Don Cullivan, why do you suppose Perry is so quick in his response?

Perry receives a letter from an old army friend, Don Cullivan, who had read about the case in the papers. Don tries to befriend Perry and convert him to the Catholic faith. Perry isn't interested in religion but welcomes the friendship. This shows Perry to be emotionally needy and, on his simple level, crave companionship.