As Quine said, there is a potentially infinite number of things that must be true (in order) for that statement to be considered true.
The simple answer is that the PP "in order" is semantically optional. Personally, I can't see any real stylistic preference one way or the other, though some speakers may consider its inclusion to be slightly more formal.
Syntactically, the subordinate infinitival clause can function as purpose adjunct itself, rather than be governed by the PP, so that's not a deciding factor either.
Note that, despite what some dictionaries say, "in order for" is not a constituent. "In order" is a preposition phrase and "for" is a subordinator introducing the to-infinitival clause for that statement to be considered true, which is a separate constituent. The infinitival clause functions as complement of the prep "in order" or, if the latter is not present, as direct complement of "true".
Note also that the clause subordinator "for" only occurs with to-infinitival clauses that contain a subject, as your example does.