What are non-parenthetical clauses called, such as an appositive? And is His, the Almighty's, saying: (for Allah will never fail in His promise) an interjection between the verb and the subject? And how can the verses in Surat Al-A'raf (And if the people of the towns… to His saying: they used to earn) be an interjection between the conjoined and the conjoined-to, despite the absence of a conjunction?

The interjection (I'tiraad) is the insertion of a phrase or statement between two connected statements for a rhetorical purpose, such as emphasis, where the removal of the inserted part does not affect the original meaning. As for the appended phrase (Tadheel), it is following one sentence with another that carries the same meaning to emphasize or clarify it.

In the verse from Al-Baqarah (2:80) "for Allah will never fail in His promise," the sentence is an interjection between (you have taken) and its counterpart (or do you say about Allah what you do not know), to emphasize that Allah does not break His promise.

As for the verse in Al-A'raf (7:97), the sentence "Did the people of the towns then feel secure" is an interjection between the antecedent (then We seized them suddenly) and the consequent.