The words inside the dome

in Saint Peter's Basilica at the Vatican

are from today's Gospel (Matthew 16:13-20):

Tu es Petrus

et super hanc petram

aedificabo ecclesiam mean

et tibi dabo

claves regni caelorum

You are Peter
and upon this rock
I will build my Church
and to you I will give
the keys of the kingdom of heaven.

(from an earlier post)