This was the last battle in which the Germans had any chance to change the outcome of the war. If they had won this battle, they might have been able to negotiate a truce instead of having to surrender unconditionally.
What the Germans were trying to do in this battle was to push their way up to the North Sea at such Belgian ports as Antwerp. Once they got there, they figured that the Allied forces would be cut in half and would be unable to really coordinate to defeat Germany. At that point, Hitler thought that he would be able to negotiate some sort of peace settlement.
Once the Germans lost this battle, their last hope was gone and they were sure to have to surrender unconditionally.