paramount: 52.Bc5!, Nimzo pointed out precisely.
This could be Saturday puzzle but if you know the theory, you would solve it with just a bit sweat.
Nimzo himself in his famous book mentions that there are 5 special cases about rook/rooks in the 7th rank. And this position could be applied for the first rule :"7th rank absolute". That means "our control is such that the enemy king is shut behind it", that means rook in the 7th rank and there are assorted threats from this position.
You see that 54.f7 its a very good move, but to be easier, its the same case that you take the absolute position first so
54.Rb7! (this absolute) and the rest is about the same with the actual line, i'll give one
The outset 52.Bc5! is a MUST. The offshoot 53...Rf7? becomes impossible because 54.a7! with the mating threat Rb8 and the rest is a cakewalk.