to breathe with both lungs, which he meant the western and eastern traditions, latin and greek traditions. so, it, too, therefore, is a symbol of unity and universality. >> yes. and in the gospel of t, doubtin thomas put his hand on jesus's wound so he wouldn't bleed, so it has to do with believing in miracles in some sense. >> and we'll also hear readings from the acts of apostles. catholics believe that their bishops, and certainly their popes, are successors of those early apostles that christ called to lead the church. we talk about apostolic succession, this kind of unbroken chain over 2,000 years of which all three of these popes, john xxiii, john paul ii, now pope francis, participate in that succession of tapostles. >> delia gallagher and john allen know exactly what they're talking about, our vatican experts just outside of vatican