These verses are the beginning of the editorial insertion that consists of verses 7–12. The beginning of verse 7 is actually part of the planned text, and perhaps the statement that “they should come forth even unto the land of promise.” However, the mention of the land of promise triggers the aside. The remainder of verse 7 describes that promised land as “choice above all other lands, which the Lord God had preserved for a righteous people.”
That statement leads into the covenant made with the brother of Jared, that “whoso should possess this land of promise, from that time henceforth and forever, should serve him, the true and only God, or they should be swept off when the fulness of his wrath should come upon them.” That is essentially the same covenant made with Lehi. It is a statement that God would lead people to this new land, and that they would be preserved if they remained faithful, but if they did not, they would be destroyed.