(17) For your God יהוה is God supreme and Lord supreme, the great, the mighty, and the awesome God, who shows no favor and takes no bribe, (18) but upholds the cause of the fatherless and the widow, and befriends the stranger, providing food and clothing.— (19) You too must befriend/(lit. love) the stranger, for you were strangers in the land of Egypt.
how long shall the wicked exult, (4) shall they utter insolent speech,
shall all evildoers vaunt themselves? (5) They crush Your people, O LORD,
they afflict Your very own; (6) they kill the widow and the stranger;
they murder the fatherless,
The correct interpretation appears to me to be that He is saying: “Do not wrong a stranger or oppress him, thinking as you might that none can deliver him out of your hand; for you know that you were strangers in the land of Egypt and I saw the oppression wherewith the Egyptians oppressed you, and I avenged your cause on them, because I behold the tears of such who are oppressed and have no comforter, and on the side of their oppressors there is power, and I deliver each one from him that is too strong for him. Likewise you shall not afflict the widow and the fatherless child, for I will hear their cry, for all these people do not rely upon themselves but trust in Me.” And in another verse He added this reason: for ye know the soul of a stranger, seeing ye were strangers in the land of Egypt. That is to say, you know that every stranger feels depressed, and is always sighing and crying, and his eyes are always directed towards G-d, therefore He will have mercy upon him even as He showed mercy to you, just as it is written, and the children of Israel sighed by reason of the bondage, and they cried, and their cry came up unto G-d by reason of the bondage, meaning that He had mercy on them not because of their merits, but only an account of the bondage [and likewise He has mercy on all who are oppressed].
מאי שנא מאנה דכתיבי שלשה לאוין (שמות כב, כ) וגר לא תונה (ויקרא יט, לג) וכי יגור אתך גר בארצכם לא תונו אותו (ויקרא כה, יז) ולא תונו איש את עמיתו וגר בכלל עמיתו הוא לוחצו נמי שלשה כתיבי (שמות כב, כ) ולא תלחצנו (שמות כג, ט) וגר לא תלחץ (שמות כב, כד) ולא תהיה לו כנושה וגר בכלל הוא אלא אחד זה ואחד זה בשלשה
Babylonian Talmud, Bava Metzia 59b:13
The Gemara asks: What is different with regard to verbal mistreatment, that three prohibitions are written concerning it: “And you shall neither mistreat a convert” (Exodus 22:20); “And when a convert lives in your land, you shall not mistreat him” (Leviticus 19:33); “And you shall not mistreat, each man his colleague” (Leviticus 25:17), and a convert is included in the category of colleague? With regard to one who also oppresses a convert as well, three prohibitions are written: “And you shall neither mistreat a convert, nor oppress him” (Exodus 22:20); “And you shall not oppress a convert (Exodus 23:9); “And you shall not be to him like a creditor” (Exodus 22:24). This last prohibition is a general prohibition, in which converts are included. Consequently, it is not correct that one who oppresses a convert violates only two prohibitions. Rather, both this one, who verbally mistreats a convert, and that one, who oppresses him, violate three prohibitions.
R' Yitzchak Hutner (1906-1980), Pachad Yitzhak Pesach 8
And when the Rambam further adds that the Holy Blessed One Godself loves the stranger, he means to prove this fundamental point, for this is the language of the verse: “Who does justice for the orphan and the widow, and loves the stranger.” See that the stranger is clearly set apart from the orphan and the widow: In the case of the orphan and the widow, the verse says, “God does justice;” but in the case of the stranger, it specifically says, “God loves the stranger.” And if love of the stranger came about only because they are most in need of love, then the verse would not have needed to separate them from the widow and the orphan. This is what the Rambam means by saying that the Holy Blessed One Godself loves the stranger, on account of what we have seen here, that the idea of such love is reserved specifically for the stranger and not the orphan and widow. Thus we learn that love of strangers is a pure love.
Rabbi Jonathan Sacks, Mishpatim: Loving the Stranger (2008)
Dislike of the unlike is as old as mankind.This fact lies at the very heart of the Jewish experience. It is no coincidence that Judaism was born in two journeys away from the two greatest civilizations of the ancient world: Abraham’s from Mesopotamia, Moses’ and the Israelites’ from Pharaonic Egypt. The Torah is the world’s great protest against empires and imperialism. ... [their] most serious offense – for the prophets as well as the Mosaic books – was the use of power against the powerless: the widow, the orphan and, above all, the stranger.
To be a Jew is to be a stranger. It is hard to avoid the conclusion that this is why Abraham is commanded to leave land, home and father’s house; why, long before Joseph was born, Abraham was already told that his descendants would be “strangers in a land not their own”; why Moses had to suffer personal exile before assuming leadership of the people; why the Israelites underwent persecution before inheriting their own land; and why the Torah is so insistent that this experience – the retelling of the story on Pesach, along with the never-forgotten taste of the bread of affliction and the bitter herbs of slavery – should become a permanent part of their collective memory.
It is terrifying in retrospect to grasp how seriously the Torah took the phenomenon of xenophobia, hatred of the stranger. It is as if the Torah were saying with the utmost clarity: reason is insufficient. Sympathy is inadequate. Only the force of history and memory is strong enough to form a counterweight to hate.
Why should you not hate the stranger? – asks the Torah. Because you once stood where he stands now. You know the heart of the stranger because you were once a stranger in the land of Egypt. If you are human, so is he. If he is less than human, so are you. You must fight the hatred in your heart as I once fought the greatest ruler and the strongest empire in the ancient world on your behalf. I made you into the world’s archetypal strangers so that you would fight for the rights of strangers – for your own and those of others, wherever they are, whoever they are, whatever the color of their skin or the nature of their culture, because though they are not in your image – says G-d – they are nonetheless in Mine. There is only one reply strong enough to answer the question: Why should I not hate the stranger? Because the stranger is me.
Tikva Frymer-Kensky, Reading the Women of the Bible (2004)
With regard to Sarah's treatment of her slave Hagar:
We like to believe that the experience of suffering makes us more sympathetic to the suffering of others. It does not. Sarai’s own experience as a slave does not make her more empathic to the slave in her own home. On the contrary, it makes her want to assert her dominance and authority so she won’t lose it again. As usual, the biblical narrator does not comment on the actions: It is left to the reader to note how easily the oppressed can become oppressors. When God raises high the lowly, how will the newly empowered behave toward those who lack power and autonomy?