It's hard to overstate the importance of loose pieces in chess—noticing them, creating them, and exploiting them. Loose piece = target. Here White sees two in the enemy camp: the rook on c8 and the bishop on h6. His immediate thought is to pair an attack against one of them with an attack on Black’s king, or to attack the two of them at the same time. The natural weapon for either purpose is the queen. It's well-positioned for action on g3. White looks for a square from which his queen could take advantage of the loose Black material and sees that Qh3 aims the queen at both bishop and rook. The only hitch is the pawn in the way on e6. The usual procedure for removing a bothersome pawn is straightforward: take something it protects. Thus White begins with RxB, inviting the recapture e6xR; now Qh3 forks the loose Black pieces and takes one of them next move, winning two pieces for a rook (and leaving White ahead by a whole piece, as he already was up the exchange).
It all would be even better, by the way, if White’s rook were on d1 instead of d2. In its actual position here White’s rook is en prise to the bishop on h6; so if White starts with Qh3, Black has BxR. If the rook started on d1 there would be no such threat and White could make Qh3 his opening move. The move isn’t quite a fork, but it threatens the loose bishop on h6 and also pins the pawn on e6, thus creating a fresh loose piece on d5. Black most likely would respond by moving the h6 bishop to safety on f4 (Kg7 is another possibility); and then White can play RxBd5, winning a piece cleanly since Black won’t recapture (if Black does play e6xR, White has QxR and still has the piece). We will examine the creation and use of this sort of pinning move in a later section of this project.