Lesson
White to move. Main line: 1. e4 e5 2. Nf3 d6 3. d4 Bg4 4. dxe5 Bxf3 5. Qxf3 dxe5 6. Bc4 Nf6 7. Qb3 Qe7 8. Nc3 c6 9. Bg5 b5 10. Nxb5 cxb5 11. Bxb5+ Nbd7 12. O-O-O Rd8 13. Rxd7 Rxd7 14. Rd1 Qe6 15. Bxd7+ Nxd7 16. Qb8+ Nxb8 17. Rd8#
Morphy does not attack because he has moved the queen early; he attacks because both rooks, both bishops and the queen reach open lines while Black’s kingside remains undeveloped.
The exchange sacrifice 13.Rxd7! removes the pinned knight’s support and brings the other rook to d1. By 16.Qb8+!, the queen’s only remaining job is to force ...Nxb8 and clear d8.
The finish 17.Rd8# is memorable, but the first fifteen moves are the lesson: develop, open the center when the opposing king is uncastled and make every tempo contribute to the attack.
Chess in a theatre box
Paul Morphy played this in 1858 in Paris, in a box at the Italian Opera, against two opponents consulting together: the Duke of Brunswick and Count Isouard. He was watching the performance at the same time.
The circumstances are half the reason it is famous. The other half is that it is the cleanest demonstration of opening principles ever recorded, and it is short enough to remember in full.
Every move develops, and nothing repeats
Morphy brings out a new piece almost every move, castles early, and never moves the same piece twice without a concrete reason. His opponents spend their moves on pawns and on a queen that ends up in the way.
By the time the attack lands, White has effectively been playing with a larger army for ten moves — not because material was won, but because Black’s pieces were still at home.
Why it is taught to beginners
The final combination is a rook sacrifice followed by mate with the two remaining pieces. It is spectacular, but it is also the arithmetic consequence of everything before it.
That is the pedagogic value: a beginner can see the reward for developing pieces arrive in the same game, which almost never happens in their own play.
Develop a new piece with each move in the opening. The Opera Game is what happens when only one side does.
Get the king out of the centre before opening lines — Black’s king never left, and that decided it.
Moving the same piece twice in the opening costs a move you will want back later.
Source: The Opera Game — https://en.wikipedia.org/wiki/Opera_Game
Source: Paul Morphy — https://en.wikipedia.org/wiki/Paul_Morphy