Philip found Nathanael, and said to him, "We have found him, of whom Moses in the law, and the prophets, wrote: Jesus of Nazareth, the son of Joseph."
Jesus called Nathaniel an "Israelite indeed," meaning that he was of the "seed of Abraham," that is, the spiritual seed, and not merely of fleshly descent.  This distinction between the genuine children of Abraham and the fleshly nation that claimed the patriarch as their ancestor is overwhelmingly significant and formed the major premise of Paul's letter to the Romans.  By such a designation, Christ implied that it was something unusual and that the vast majority of the outward Israel were not true sons of Abraham.