Ulhumbrus: Reshevsky's comment on the move 18...Nac5 is < 18...Nac5! Black offers a pawn which White unwisely accepts>
On the move 19 gxh5 to quote from his remarks < 19 gxh5? Correct is 19 Ba2 and Black has to play very precisely to keep out of trouble...>
Reshevsky's comment on the move 22...Ne5 is < By giving up a pawn, Black has the initiative. The two bishops and the exposed position of the White King are more than sufficient compensation for the pawn sacrificed>
This suggests the following question: Why does White's acceptance of the pawn transfer the initiative to Black?
If we look at the position after the move 22...Ne5 we can see that Black has removed White's king's bishop so that it no longer controls the square g8.
Black's King enjoys therefore the use of the square g8 as a flight square, so that the check Qh4+ is no longer much of a threat.
With White's KB controlling the square g8, the move Qh4+ would indeed be a threat.
Thus the loss of potential control of just one flight square around Black's King - an important flight square, however, as it is the only one Black's King has - has the effect of transferring the initiative from White to Black.