for a communist party itself, illegal work is primary, and legal work secondary (all must be relatively clandestine). for the mass organizations generated by a communist party, legal work is primary, and illegal work secondary.
before revolutionary war is initiated, legal work is generally primary (at least for as long as the state allows any work to be legal), and illegal secondary. so during this period, most work will be undertaken through the mass organizations, rather than through the party itself or any embryo of an army that may exist
after the nodal point that is initiation of war, illegal work is primary, and most mass work will be done through the army
it is an error to confuse the secondary for the primary, but it is also an error to treat the secondary as if it is of no importance
mao teaches us that before war is intiated, all mass work serves to prepare for it, and during people's war, all mass work is in service of the front
the aforementioned dynamics shift in a fashion typical of dialectics - not linear, and also not a binary, but gradual quantitative shifts that eventually beget a quantitative shift, at the nodal point which is initiation
this is because, for one, the movement will necessarily be gaining strength as initiation approaches (tautologically so), with more of the masses behind it willing to go further, so the bounds of bourgeois legality must be stretched ever further in preparation for revolution (both to train the masses in war, and in a practical sense, like with expropriations and land takeovers)
additionally, as capitalism falters and as the proletariat rises, the old state will grow increasingly repressive, furthering the need for clandestinity and for combatting political police
in mao speaks of the non-militarized mass struggle in "capitalist countries that are not fascist or at war," and his advice for the present, but it is extremely unlikely that we will make it all the way to initiation without the bourgeoisie unleashing an inter-imperialist war and/or the full force of fascist repression
and when that repression comes, we will require a clandestine, professional (in the sense lenin means it, which is measured in ability to combat political police), bolshevik style communist party. which necessitates building its infrastructure and training for it right now, without negating the current primacy of the mass legal struggle