Verses 3–7 are grammatically awkward. For those wanting to make more sense of the verses, simply read verse 3 without the “as,” and it will work better.
The point of the verses is more important than their grammar. Amulek notes that they should have been taught of the coming Messiah. Alma had taught them the principles of developing faith, and had introduced the topic of the coming Messiah by turning to the scriptures, specifically the words of Zenos and Zenock, both prophets whose writings were recorded on the brass plates.
That synopsis of what Alma had taught them prepares Amulek for what he wants to teach them in the next verses.