Exodus 23:9
Also thou shalt not oppress a stranger: for ye know the heart of a stranger, seeing ye were strangers in the land of Egypt. Also thou shalt not oppress a stranger: for ye know the heart of a stranger, seeing ye were strangers in the land of Egypt.
The verse belongs to the instruction given to Moses on the mount in Exodus 19-24, which is truth and light and grace in Christ, and to the statutes that protect the poor and guard the interests of the people. Moses was to gather up that instruction and carry it out in practice before the people as an example of obedience to the whole of the commandments. The stranger is one who has joined Israel, and the command forbids oppressing him, guards against doing injustice, guides dealings with one another, and requires protecting him from wrong.
The ground of the command is Israel's own experience, for having been strangers in the land of Egypt they knew the heart of a stranger. That knowledge was to lead to compassion, with softened and subdued hearts, loving as brethren and letting all contention cease. It was given by Christ Jesus, the same Teacher who gave the directions on Mount Sinai and who has spoken in human flesh. It is to be studied and presented before the people and obeyed from the heart, being needed now just as verily as by Israel in the days of Moses.
Keeping it with the other commandments carries God's condition that the obedient shall be as kings and priests to God, with God communicating to them and they communicating with God. That reward was held out to Israel then and is still held out now. Israel with uplifted voice and hands pledged to comply with the conditions, yet when temptation came in Moses' absence they failed and made the calf.