I’ll make this the last Ruy Lopez for a little while, but once again it’s a deeply instructive one. Defending the Closed Spanish Black defends against White’s threatened attack by massing his pieces on the kingside (14…Ne8, 15…g6, 16…Ng7 and 17…f6 are key moves in the construction of his defensive formation). Later on Black also breaks out with 21…f5, taking the initiative in the same way Black can in the King’s Indian Defence.
Nowadays we are of course familiar with this plan, but at the time it was still being worked out. There were no computer databases to help masters figure these things out, that had to use their own brains together with the board and pieces.