Note the "wherefore." The causality from one clause moves to the result in the next. The softening of the hearts of the Gentiles and their joining with Zion becomes the mode through which the consecration of the land occurs for the Nephites. Isn't Jacob saying to his audience that the influx of Gentiles into their midst, and the prediction of salvation at the hands of the Gentiles, will be the way in which this prophecy is fulfilled? Assuming that context provides tremendous power to Jacob's message for community unity.