Jamieson, Fausset and Brown on Leviticus 19:33-34

33-34. if a stranger sojourn with thee in your land, ye shall not vex him--The Israelites were to hold out encouragement to strangers to settle among them, that they might be brought to the knowledge and worship of the true God; and with this in view, they were enjoined to treat them not as aliens, but as friends, on the ground that they themselves, who were strangers in Egypt, were at first kindly and hospitably received in that country.