That is simple: they keys are obviously the gospel, as it is by faith in the gospel of Scripture that believers have been delivered from the power of darkness, and translated into the kingdom of his dear Son. (Colossians 1:13)
It is Rome that befits Christ's words: Woe unto you, lawyers! for ye have taken away the key of knowledge: ye entered not in yourselves, and them that were entering in ye hindered. (Luke 11:52)
For her gospel of salvation usually begins with being formally justified by one's interior holiness via sprinkling in recognition of proxy faith, and usually ends with becoming good enough to enter glory via purgatory. This is not the gospel Paul preached, and thus those that preach are accursed. (Gal. 1:6-9)
Well put!!