"This" via "It"

[Tom]

Hi

[Mister Micawber]

.
Too general to deal with comprehensively, Tom. 'This' (along with 'that', 'these' and 'those') is deictic, referring to a spatial position in the contextual world outside of the sentence. 'It' is a non-spatial-referential (my term!) pronoun.

Your red words are fine.

PS: 'vs' not 'via'.
.
_________________
Native English teacher at Mister Micawber's

[Tom]

[Mister Micawber]

.
This is a pencil -- The speaker must be pointing to the pencil, or otherwise indicating it in some way, in reality outside the sentence.

It is a pencil -- the pencil need have no location and in fact no specific existence.
.
_________________
Native English teacher at Mister Micawber's