The 320 is not tuned to takeoff or land in normal law so it needs to blend its laws from ground law to normal law on takeoff and when landing it blends back to ground law which happens in the flare mode.
Lot's of things happen in the flare mode, have you ever tried to land in normal law with no flare mode, it gets REEL interesting, you pull back on the stick to flare and you go back into the air. If you happen to get it on the ground and pull back on the stick, the nose will jump up on you, increasing the possibility of a tailstrike.
Plus you get no reverser's if landing with NO flare mode.
Hope this helps