CHICAGO – In a meeting room under Holy Name Cathedral, a rapt group of black Roman Catholics listened as Barack Obama, a 25-year-old community organizer, trained them to lobby their fellow delegates to a national congress in Washington on issues like empowering lay leaders and attracting more believers.

“He so quickly got us,” said Andrew Lyke, a participant in the meeting who is now the director of the Chicago Archdiocese’s Office for Black Catholics. The group succeeded in inserting its priorities into the congress’s plan for churches, Mr. Lyke said, and “Barack Obama was key in helping us do that.”