This is not strictly necessary, but is the normal and general way to take a paragraph of information. To depart from a parallel or same sense we need some reason. Here we do not. See the good grammars and lexicons for this. We may rule out direct discourse.
Indirect discourse does fit the context.
It is true that unbelief is sin. The clause in each case clarifies or completes the object of the preposition in our context. The problem remains that these then need further clarification themselves. They are too ambiguous. Also, the clarity of each segment is uneven.