R. Shimon says: If one became a proselyte between the two Pesachs (Pesach rishon and Pesach sheni), I might think he offers the second Pesach; it is, therefore, written "and he shall be as the citizen of the land." Just as the first, who did not offer the first (though normally being obliged to do so), offers the second, so, a proselyte, who did not offer the first offers the second, (to exclude one who became a proselyte between the two Pesachs, who was never obliged to offer the first Pesach.)