Black is waiting for his opponent's action, since not much else can be done. White can't improve his position much, all his pieces have great positions, therefore, it's time to look for a break. 46.h4 and White wins. Accuracy is always important. 45.Rd2 Ke7 Black is barely holding and any move would make his position even worse.
Bishops are always great when there is a moving pawn pair, or three connected pawns.
In such cases Bishops stand behind, supporting pawns, or attack squares ahead of such pawns, supporting their move forward. In this position the center is closed, but there are some open diagonals. White's goal here is to make the game more open, plus he should also keep his eye on the Kingside. Petrosian starts shaking opponent's position up. Almost a decisive mistake.