David Mangan looks back on a retreat held 50 years ago this weekend as a life-altering event. And not just for him. Roman Catholics throughout the world are still feeling the effects of the spiritual movement launched by the small gathering at a retreat house about 15 miles north of Pittsburgh. Mr. Mangan, a recent Duquesne University graduate, had joined a group of Duquesne students and staff in mid-February 1967 for a three-day retreat focused on biblical teachings about the Holy Spirit. There, he was struck by a speaker's comment that when the Bible promises power to Jesus' followers, it uses the same Greek word that forms the root for dynamite. I had to come to grips with the fact that although I was a solid Catholic, dynamite was not the descriptor of my spiritual life, he said.