Rook on the seventh
A rook on the seventh rank (the opponent’s second) attacks pawns from the side and can trap the king on the back rank.
Pawns defend forward. A rook beside them attacks the base of the chain. Two rooks on the seventh often win on the spot because the king is cut off and the pawns fall.
The rook on b7 already hits a7, f7, g7, and h7 and keeps the king on the eighth rank. Black’s rook on e8 is the only piece stopping some back-rank ideas.
Getting there usually means an open file plus an invitation — a weak seventh-rank pawn or a king that has no luft. The open-file and back-rank pages are the setup; this is the payoff.