A solid and typical move. The plan is to capture the knight and gain control of the d5-square.
1. e2e4  1... e7e5  2. g1f3  2... b8c6  3. f1b5  3... a7a6  4. b5a4  4... g8f6  5. e1g1  5... f8e7  6. d2d3  6... b7b5  7. a4b3  7... d7d6 Together with 8.a4 and 8.c3, this is one the main lines of this Ruy Lopez system. 8. a2a3  8... c6a5 A known move, but much rarer than the most natural castling. 9. b3a2  9... c7c5  10. b1c3  10... c8e6 