tactics question

I was using game explorer today,and got to this point--

http://www.chess.com/explorer/index.html?id=5556&ply=33&black=0

the most common move suggested was for black to do b4.   Why not take the rook at g7 that white just moved (with black's bishop)?   why leave  white's rook there?

thanks!

jpr1

Materially speaking, it's the same thing, black threatens BxR winning 2 points of material vs threatening bxc3 which is 2 points of material and the in between move has the benefit of getting black's play going.

Although to go beyond surface value I looked it up and apparently BxR immediately fails tactically.

Nevermind, just went further in and that's refuted.  Waffle's is better

thanks!  very helpful--

yeah, interesting to see how if you do BxR, it leads to the whole left side of the board (from white's perpspective ) opening up for an attack--  

originally I thought that moving the pawn to b4 was attacking too early-- but in this case it seems not.