That is almost certainly a typing mistake. My guess is the author started to type something, and then changed it, and forgot to delete the word "will". They may have originally typed "[...] true revolutionary will be willing", without the "must", or they mistyped "will" instead of "be willing" and then did not delete it.
Also, "true revolutionary" should take an article. "a true revolutionary" is probably what was intended and is the normal construction. However, some artistic license would be allowable here to refer to an idealized abstract concept "the true revolutionary." This type of construction was common in philosophical texts of the late 19th and early 20th centuries.