Black resigned, because after 39...Bxd6 40.Qf7+ Kd8 41.Rxd6+ he is mated.

White’s entire strategy revolves around using the d5-square as an outpost for his pieces. For the sake of this, he has gone in for a positional queen sacrifice. Undoubtedly, if White manages to castle queenside, exchange a pair of knights and entrench his bishop on d5, his pawn structure will be ideal. The e4-pawn and Bd5 will defend each other, and the d3- square will be used as a transfer point to bring a rook to the queenside, to attack the black pawns there.
Therefore, Black plays a counter-sacrifice, to sow disharmony in the white position:

The white pawn, lacking piece support, is not dangerous.

This does not help, but after other continuations too, Black puts a rook on d8 and takes the d-pawn.

and Black realised his material advantage.

On the d-file, the Bd7 and Qd2 can come under fire, whilst the same can happen to the black king along the f-file. from the threat of opening these lines, after the move...

there is also a threat to bring the knight to e4.

This allows the f-file, on which the king stands, to be opened, which should not have been allowed in any circumstances. Consequently, a more tenacious defence was 22...exf5, after which the strongest resort is 23.exd6 23...Qxd6 24.Rd1 Qc7 25.Nd5 – the white attack will henceforth develop almost of its own accord.

More tenacious was 28...Kg7, after which the cleanest win is 29.Rexf6 Qxf6 30.Qd3 Rd2 31.Qg3+ Qg5 32.Rf7+ Kh8 33.Qc3+ Qe5 34.Qxd2 Qxh5 35.Rxb7.

Black resigned.