It's simple: black's N has a good spot to go: Nxb4. Now, a bad exchange is threatened. Nothing more. Another R will stand in the same place, only thing, black will have the move. When a threat like this is faced, you can 1) avoid the threat (falling into what your opponent probably wanted you to do). 2) respond with a counterthreat of the same nature, 3) Ignore the threat and take the tempo for a more important goal. All three must be considered. The rook must move? Well, no, as white has the counterthreat Nb4. Black better goes Rd7. Otherwise: NxRc1, NxRd6+, c7xN, RxNc1+, Kd7, with very bad doubled pawns for black. So white better moves the R, and the only logical square is b1 - so to protect the b4 pawn. The attack with Nb5 (forking Rd6 and a7) is still threatened, so Nb5, Ra6, Rb2 and black will have to go back with the N. Fortunately, he will be able to do that, and the game will last for long after.

White missed the whole point of sacrifying the b4 pawn! Nb5 was dued! (winning back the d pawn, at least...).

Accurately noted. Whites is waiting too much for his counterplay, that obvilusly didn't seem appealing enough to white...

yes, but if he took the pawn, i would take the rook...

then i would of taken his castle

This was a mistake, because Nb2 wasn't foreseen. White must play Rc2, here, to stop it.

I was thinking the same. It was the obvious threat. But after NxRd1, NxRd4+, NxRc3, NxNc3, Re8 (better than Rd8, Nd1), Kf2, Re1! and, if I am not wrong, black will have to lose the N to d1=Q, NxQ, RxN.

ahhh ok..... didn't see that

White already spotted the right way to proceed and get back the material without losing the Rd1. But it just doesn't work...