This is the classic Lucena position. White is definitely winning, but has a major problem to solve: His king stands on the pawn's promotion square and currently can't move. Furthermore, even if he could, repeated rook checks from behind will force him back in front of the pawn. The next sequence, famously called "building a bridge", addresses those issues elegantly.
Analysis from B.Larsen-W.Browne, Las Palmas 1982.
