WATCH: Stephen Colbert on Why He's a Christian

In a sneak peek at an upcoming interview, Stephen Colbert discusses his faith with surprising frankness.

The new host of Late Night sat down with Father Thomas Rosica, media attaché to the Holy See Press Office and CEO of Salt and Light Television.

The Daily Beast, which got a preview, writes that, "[t]he extensive exclusive interview, which is at times hysterically funny and profoundly serious, airs in full on Rosica's interview program Witness on Sept. 13."