This was more Engels, but essentially it was a way to cast a wide net and categorize/capture all the people that were not outright supportive of the cause. The big bad guy for communism was the bourgeoise but they had to account for the masses of regular people that were avers or apathetic to the ideology. During the Socialist revolution the masses had the option to became either the proletariat that would benefit from and thus supported the revolution or you would get lumped into the lumpenprolotariate and you suddenly just became too stupid/ignorant to be able to understand and must be pitied and helped. Its a psychological trick that commies still do today to gain forced support through group membership and identity politics.