Redaction: The contrast of subject in verses 16 and 17 perhaps tells us a little more of Mormon’s source material. In verse 17, the voice of the Lord comes to Alma, suggesting that Alma recorded this information and that Mormon copied it into his own record.
What is less clear is the source of the generalized communication from Yahweh to the people in verse 16. We do not know if it represents Alma’s written description or Mormon’s assumption. I read it as the communal understanding of Yahweh’s answer, which Alma likely wrote and which Mormon copied. When Mormon inserts his opinions (as with King Noah), his interpolations are quite obvious. In this case, the most likely scenario is that Alma was emphasizing his people’s spiritual preparation. They understood that Yahweh would deliver them. That it would happen “on the morrow” must be Alma’s conclusion after he began to prepare for the journey in accord with his direct revelation. While the people may have understood that deliverance was coming, it is doubtful that they would all have clearly understood that it would occur “on the morrow.” Alma appears to be taking a small literary license here as he emphasizes his people’s righteousness.