Black has now a passed pawn, and his Bishop exerts great pressure.
A “passed pawn” is one that has no adverse pawn either in front or on either of the adjoining files.
A passed pawn is mostly serviceable when supported by another Pawn.
The first thing is to find out, by counting, whether the opposing King can be in time to stop the passed pawn from Queening.
The play was based throughout on the chance of obtaining a passed pawn on the King's file, with which White expected to win.