Hard Puzzle

1k1r4/p1p2p2/BpRrp1p1/PQ1p4/3q3p/K4P2/8/1R6 w - - 2 28
This puzzle was on lichess, it is rated over 2900 and I don't know why Rbc1 is the correct move. Can anyone explain this?

I created a study to help you guys understand it. lichess.org/study/57E82O3l