Mormon focuses on his future readers. While he usually includes the Gentiles, to whom his book will come, his first interest is always in “the remnant of the house of Jacob.”
He enigmatically states that “these things”—meaning his message to the house of Israel—are written “after this manner” because otherwise “wickedness” might somehow “bring them [these things] forth unto them [the remnant of Jacob].” Therefore, something in the manner of his writing is ordained of Yahweh and influences how it will come forth. In my opinion, by “manner,” he means that Yahweh has instructed him to inscribe his record on gold plates so that the text would survive the method of delivery, which was being “hid up unto the Lord.”