At the most basic level, White's third move attacks the knight which defends the e5-pawn from the attack by the f3-knight. White's apparent threat to win Black's e-pawn with 4.Bxc6 dxc6 5.Nxe5 is illusory—Black can respond with 5...Qd4, forking the knight and e4-pawn, which will win back the with a good position. White's 3.Bb5 is still a good move; it a piece, prepares castling, and sets up a potential pin against Black's king. Since White's third move carries no immediate threat, however, Black can respond in a wide variety of ways.