6.Bg5 is probably the sharpest, but not necessarily the strongest.

6.Bc4 is the move I always have played which is very sharp.

This variation always seemed to go against my basic chess instincts. It neglects the centre and there are so many pawn moves. That seems to violate two basic opening principles. My question is, why does this opening even work??

It neglects the centre? The point of the Sicilian from the Black side is that he gets 2 centre pawns vs just 1 for White. And this is the reason Black often gets to take liberties - his d6-e6 wall gives him a lot of protection.

So whats the idea behind the sicillian? Black defends himself in the centre while expanding on the queenside? Then once he has gained space there he strikes back in the centre? Is this is initial idea?

Do you mean the point of 1...c5 rainbow? 1...c5 controls d4, so that if white plays d4 black is happy to exchange (unlike if he played ...e5 which would concede a central point, though he does at least get the e file) because he gets the c file and two center pawns. So it makes white's d4 move move double edged. The center pawns are at first used defensively but black at all times could be preparing a central counterattack at the right moment. However, if black made these kind of moves in the scotch before castling, well I imagine there would be a disaster on f7 or something while in the sicilian black may be able to play ...e6 to block out this diagonal. If white doesn't play d4, then in fact black's best setup is similar to an english one, usually with a king's fianchetto to control d4.

it's certanly f3, or Be3 and than f3

thanks for all the help

 The opening works because there is no weakness for white to attack. So his lead in development doesn't gain him anything in the initial stage. Lead in development is only an advantage and meaningful when you have a target to actually attack.

Exactly. In fact if you think the najdorf is crazy, look at the kan sicilian! Black waits even longer and develops his queen first! I like that line since black can positionally build up and white is forced to do the same usually since nothing can be cracked open in the early stages.

I believe 6. Bg5 is the sharpest per se.  One would be hard pressed to argue that there are many lines more theoretically dangerous than the Najdorf Poisoned Pawn!  That said, the English attack after 6.  Be3 or 6. f3 has so much current theory behind it that you need to be booked up to your eye balls to not get crushed.

If you are looking for sharp, the only systems I find that end up in forced draws or plain positions are those after 6. Bc4.  For almost every reply Black has, White can end up with a theoretical draw by force!  How dull, no?

As a white player unless you are Garry Kasparov Bg5 is like opening Pandora's box, far to many sharp varied openings. Almost anything in the Najdorf Sicilian is very sharp. What make it inherently sharp is that 1. It is sicilian 2. very popular opening.

This is a completely wrong assumption to begin with. The Najdorf is an opening not based on straight concepts, but more concrete lines. It is amongst one of the sharpest openings from the Black side. That being said, there are concepts behind the Najdorf but when getting deep into lines, concepts alone will not do it for you.

Somebody already mentioned the idea that Black simply accepts being behind in development and develops in such a way that leaves as few targets as possible. Most of the fighting in the Bg5 lines involve the fight for the d5 square for White, while black expands on the Queenside and often tries to control the e5 square and post a knight there.

The insanity of the opening is the subtleness of move orders. In some lines Nbd7 deserves a ! and others a ?, even though the positions may look entirely similar.  In others, h6 is either amazing or a failure.

I recommend Kasparov's DVDs on the opening to anyone wanting to see a nice history and survey of lines.