7.f4 in the French Defense (Steinitz Variation)?

Hi guys,

First off let me say that I suck at openings. But I just can't figure out this Steinitz Variation out of the French Defense (C14).

Im currently at this position (diagram below) in a game im playing, and opened the explorer to help me find my next move, since Im not familiar with this opening. Turns out 7.f4 is by far the most popular continuation (picture below), but I just don't understand why. Why not continue developing my minor pieces? Both have pretty save squares. And most importantly, why ruin the kingside pawn structure this early in the game if I want to castle kingside?

I would love to hear your thoughts of this variation and find out why 7.f4 is supposingly so logical.

Cheers!

I've been looking a little at the French.

Yes, there is a weakening around the king but it does support the pawn on e5 and prepares f5 and a kingside attack where black usually castles.

The question with this opening seems to me is "which side is white going to castle on ?" and it seems that leading up to this, each side doesn't know, but never the less must make useful moves until this question is resolved. (perhaps like in the KID ?)

One idea is that f4-f5 chould be useful later. 7Nf3 is respectable too after 7....c5 8d4xc5 Bxc5 9Bd3 f6 10pxp Nxf6 white's centre is gone, and has to rely on peice play. So that's another point of f4, of course to help defend e5.