The term, "isles of the sea," is a term which Nephi has use to refer to the land of promise. In this passage, the Lord uses it in a similar fashion. Although we think of the Americas as two great continents, it is completely natural that Nephi, having sailed to the promised land, should refer to it as an isle of the sea, we have been led to a better land, for the Lord has made the sea our path, and we are upon an isle of the sea. But great are the promises of the Lord unto them who are upon the isles of the sea; wherefore as it says isles, there must needs be more than this (2 Nephi 10:20-1). Every time Nephi refers in a prophesy to the "isles of the sea," he is thinking about the land of promise. When the Lord says, I remember those who are upon the isles of the sea, He is referring to the Nephites, among others.