DEAR READERS OF GH REFERRED HERE: Read carefully. This post has nothing to do with rationalism and mitzvos. Check here for a full list of mekoros on Orthopraxy, the lack of belief in G-d. When the Rambam says one must believe in G-d “Ani Ma’amin”, when the Torah says “Anochi Hashem Elokecha”, that is a positive mitzvah, not just a lav prohibiting denial. According to some Rishonim it is axiomatic and therefore is not even counted as a mitzvah! Even a nochri who observes mitzvos but does not believe they were commanded by G-d at Sinai does not get olam haba, as Rambam writes end of ch 8 of Melachim. Note that not a single source that says otherwise has been offered - just armchair philosophizing. See here
Your doctor refers you for surgery and recommends a person who he things is a highly skilled surgeon. You visit the office and notice on the wall a diploma from Zulu’s School of Quackery. Although he was recommended, your suspicions are aroused, so you decide to have a little conversation before entrusting your care to this guy. “Scientific method? – Don’t believe that for a second – it all depends on the spirit world.” Not too reassuring. “Post operative care – yes, I’ll give you antibiotics, but those don’t really kill germs, they just invoke the spirit world to rest on the wound and draw off the evil.” You are getting more nervous. “Sterilization – of course, for how else would the good sprits be able to dwell on the scalpel?” Uh-oh.
Scientist or quack? You make the call.
You see, handling a scalpel is not all there is to being a doctor. A doctor is trained in science, which has a whole range of philosophical assumptions about the world as well as a methodology to test truth and falsehood and a means to advance knowledge. A quack who can handle a scalpel is nothing more than a quack imitating a doctor, but not the real thing. He cannot advance the field of science, because he does not understand what science is. He cannot determine what is essential and what is secondary, because he does not understand the why, only the what. His approach is a superficial parody of what scientific training is all about.
Orthopraxy is the imitation of Judaism. It parodies the practice of Judaism without subscribing the philosophical beliefs and underpinnings of the real thing. As the Chovos haLevavos devotes his entire sefer to establishing, in authentic Judaism explicit practice is just a means of revealing the heart. Or, as Chazal put it, ‘Rachmana liba ba’i’. Judasim is not just a means to a more ethical society, a more complete personal ethic, a more refined way of life - those are just nice side products of the -praxy side of the coin, but are not the telos of religion. The telos is nicely summed up by R' Tzadok haKohen's statement that all mitzvos aseh really come to teach one principle, and its a -doxy one: "Anochi Hashem Elokecha". Without belief, the rest is just going through the motions.