1. When reading Russell's arguments about how philosophy is different from science we can see that for him science exposes a fact and the factors that compose it, without it being necessary for the public to reason about it, that is, science offers a specific and immutable information. Philosophy, on the other hand, has no specificity and requires the public to reflect on the concepts exposed by it, reason and come to a conclusion that will be individual for each individual. In other words, for Russell science works with facts, while philosophy works with reflection and that is what establishes the difference between the two.
2. He says that this difference is good and that it allows science and philosophy to each have their value in relation to the topic addressed. It also shows that society is only the way we know it today because the difference between science and philosophy is stimulated and allows them to complete each other and promote the advancement of society.
3. When he talks about "prejudice" and "common sense" he wants to show the inverse relationship that these two concepts have. If one exists, the other cannot exist and it is necessary for society to encourage the existence of one in the name of the detriment and extinction of the other.