CATHOLIC CHURCH
For those who may be wondering about the interior of this basilica, St. Paul's is a Greek Melkite (Catholic) Church. Its liturgy comes from the Church at Constantinople. The divider screen you see behind the pope is called an iconostasis, a wall of icons and religious paintings, separating the nave from the sanctuary in a church. From Wikipedia:
A direct comparison for the function of the main iconostasis can be made to the layout of the great Temple in Jerusalem. That Temple was designed with three parts. The holiest and inner-most portion was that where the Ark of the Covenant was kept. This portion, the Holy of Holies, was separated from the second larger part of the building's interior by a curtain, the "veil of the temple". Only priests were allowed to enter the Holy of Holies. The third part was the entrance court. This architectural tradition for the two main parts can be seen carried forward in Christian churches and is still most demonstratively present in Eastern Orthodox churches where the iconostatsis divides the altar, the Holy of Holies containing the concecrated Eucharist - the manifestation of the New Covenant, from the larger portion of the church accessible to the faithful. In the Eastern Orthodox tradition only men can enter the altar portion behind the iconostasis.
The iconostasis is retained by those Catholic Churches who retain a Byzantine liturgy.