How could Israel, living in its own land with a king, call itself "strangers"?

David says it of himself and the people together: "For we are strangers before you and foreigners, as all our fathers were. Our days on the earth are as a shadow, and there is no remaining" (29:15). He says it before you, before the LORD, and he sets it beside the shortness of life. The Law had already put it this way. The LORD told Moses about the land, "The land shall not be sold in perpetuity, for the land is mine; for you are strangers and live as foreigners with me" (Leviticus 25:23). In Hebrew these are the same two words as 29:15, gerim and toshavim (tap strangers and foreigners). David's prayer also says whose everything is: "all that is in the heavens and on the earth is yours" (29:11). The chapter doesn't explain the words further.