The two wingers, whose scintillating form last term took Bayern to a Bundesliga and DFB-Pokal double and the final of the Champions League, played a starring role in the 4-0 win over Hoffenheim.
"They are incredibly important for Bayern Munich, as Messi and Xavi are for Barcelona, or Ronaldo and Ozil for Real Madrid," Van Gaal said.
"With Robben and Ribery, we have more creativity going forwards. We have had to wait six months for them to be back."
During that time, Bayern have slipped 13 points behind league leaders Borussia Dortmund, but with Ribery and Robben back, they now have a glimmer of hope of successfully defending their title.
"The decisive months are still to come," Van Gaal said.
Director of sport Christian Nerlinger added: "I think this is a good start to some very important weeks. That was very impressive. Of course Ribery and Robben are players who can put the cherry on top."