"You shall not oppress a sojourner. You know the heart of a sojourner, for you were sojourners in the land of Egypt." (Exodus:23:9)
It's interesting how perspective can change a perspective. Often, when I think of my past experiences––where I came from, who I once was––it helps me to have a greater appreciation for where I, by the grace of God, am now. It also allows me to have a greater understanding for others.
This is what God is getting at in Exodus 23. Laws are being doled out like candy on Halloween night to the nation of Israel, who has just been set free from slavery in Egypt. God, in his infinite wisdom, knows that the temptation for Israel will be to think they are something special because they've been set free. If their hearts and minds go in this direction, it would hinder the way they view people who are not Israelites. It's in light of this, that God reminds them, "You were sojourners..."
It's a reminder to me that I am not a privileged person. I, though born and raised in "the land of the free," have no greater privilege than the person who just immigrated here a week ago (speaking from a purely human standpoint).
God, when he looks on humanity, sees people who are made in his image. He doesn't care what the color of their skin is, what country they are from, or the language they speak. He simply sees people.
Jesus, when he came to live on this earth, came with the purpose of dying on a cross––for the world. That is, Jesus came for the purpose of dying so that people from all nations, and with all sorts of backgrounds, would be able to experience the freedom he alone can give, and which not a single human deserves.
Don't forget who you were. Jesus came to reverse the order, the way in which a fallen world views humanity. Because of Jesus, we no longer look at people in regards to anything other than who they are, or might become, in Christ.
I too was a sojourner, a man lost and wandering around hoping to be given freedom and acceptance by the only one who can give it. That freedom came, not because I found it, but because God, in his grace, pursued me through his Son, Jesus.