It doesn't say illegal, it says good Samaritan blocking of objectionable material. If it doesn't have anything to do with curation (publisher) vs firehose then

It doesn't say illegal, it says good Samaritan blocking of objectionable material. If it doesn't have anything to do with curation (publisher) vs firehose then what does this mean: > No provider or user of an interactive computer service shall be treated as the publisher or speaker What is a publisher and why do they need to say this? What distinction is there? Were they treated as a publisher before Section 230?