ויקם אברהם מעל פני מתו וידבר אל בני חת לאמר: גר ותושב אנכי עמכם תנו לי אחוזת קבר עמכם ואקברה את מתי מלפני
(בראשית כ"ג, ג'-ד')
The parasha called "The Life of Sarah" begins with the death of Sarah. Avraham, after the period of mourning, sets about to find a suitable burial spot for his dead wife. He turns to the people of Chet, residents of the land, and says to them:
"I am a stranger and a sojourner with you: give me a possession of a burying-place with you, that I may bury my dead out of my sight."
(Bereshit, 23, 5)
The words Avraham uses to describe himself - stranger (ger) and sojourner (toshav) - require some investigation. Why would Avraham label himself both a stranger and a sojourner? Perhaps we can learn a few things from this choice of words by Avraham.
Rashi, and many other commentators, explain that Avraham wanted to stress the fact that, although he is a stranger to the land, his intentions are to become a sojourner, a permanent resident. Therefore, his claim to be allocated a plot of land for burial purposes, something which a passing stranger cannot ask for, is justified. The Or HaChaim expands on this explanation by claiming (somewhat asynchronously) that Avraham was relying on the halacha that one is allowed to give a "ger toshav" a permanent gift, and that this halachawas binding also upon the people of Chet. Giving a burial plot to someone who has emigrated to live among you is considered "the done thing", part of the Natural Law; the halacha merely restates this law. Avraham demonstrated his friendly and neighbourly ways, for example by fighting the four kings to liberate the people of Sodom or by his insistence to take nothing from Avimelech, so he was right in expecting the locals to reciprocate in a fair and friendly manner.
But Rashi provides a further explanation. He quotes the Midrash that says that Avraham was in effect threatening the people of Chet: if you do not accept me as a stranger, I will take the land by force as a sojourner; it is rightfully mine, as was promised to me by God. Why would Rashi bring this Midrash? To understand this, we need to recall the first Rashi on the Torah, which quotes another Midrash: Why did the Torah start with the Creation story and not with the first mitzvah given to the People of Israel? Because nobody has an inalienable right to the land; the "promised land" is not a promise that is kept without any conditions. In fact, it depends on the will of God. When the people deserve the land, by walking in God's ways, they get it; if not, they don't. And indeed history proves this: the current situation, where Israel has been independent for almost 60 years, is an aberration in the thousands of years of Jewish history.
So Rashi is perhaps trying to tell us that although we have a divine promise to inherit the Land of Israel, this is a right that we cannot claim by force no matter what. Avraham's veiled threat comes with the plea of being a stranger that has demonstrated his willingness to live peacefully in the new land. Yes, the land has been promised to Avraham, but he knows he also needs to deserve it.
A final thought about the use of "stranger and sojourner" is from Rabbi Lichtenstein, who uses these words of Avraham to describe the existential dilemma of every human being. As humans, as lives are finite and we do not know when we will die. And yet at times we act as if we we will live for ever, making long-term plans and feeling (over)confident about ourselves. This paradox is highlighted by the story from Berachot: the sages were at a party and asked R. Himnuna to sing a song. He stood up and sang about how terrible is the day of our death (talk about a party spoiler). When asked by the stunned sages how they should respond to this, R. Himnuna answered that they should sing about our faith in God and his laws. By acting like he did. R. Himnuna illustrated not only the paradox of our short lives (we are "strangers" on this earth) coupled with our tendency to feel invincible (as real "sojourners"), but also the remedy for this existentialist conundrum: attach yourself to the real sojourner, the eternal one, in order to get by this life.
In summary, Avraham's use of the expression "ger ve'toshav" to describe himself teaches us a few things: that we should act in a neighbourly and honourable manner with the residents of the land; that we should not think our right to the land is unconditional, as it depends on our behaviour; and that to survive in this world we need to attach ourselves to God.