I came across this puzzle and even after I learned the answer I couldn't quite understand what's going on. I understand that we amaterial advantage by capturing the knight with a pawn, but I can't understand why the queen has to go to d8. Can someone please explain the answer?
[FEN "r1b2rk1/1pqpbppp/p3pn2/6B1/3NP3/2N2Q2/PPP2PPP/R3R1K1 w - - 0 1"] 1. e5! Qd8 2. exf6