The actual Exodus proper within the text of the narrative composed by Moses represents such a small section that one could miss it easily if he or she skims the page. Interestingly, Moses shows much more concern about the meaning of the event as it relates to the Passover than he does the actual fast-paced exit from Egypt.
Of course, the people do make a hasty exit with their kneading bowls perched upon their shoulders. One might not expect, however, the composition of the people who leave the land of Egypt to eventually enter the wilderness and receive the Law at Sinai. Generally, when we imagine this event, we think of a pretty homogeneous group of people: the people of Israel. Or, we might think of them as the people who would become the Jews of the late Old Testament into the New Testament. That’s not entirely wrong, but it does not prove entirely correct either.
Notice verse 38: A mixed multitude also went up with them, along with flocks and herds, a very large number of livestock, (NASB, emphasis added).
These people do not spring from Jacob only. Some of them descended from Mizraim of Genesis 10:6. Mizraim produced the people of Egypt (often translators render “Mizraim” as “Egypt”). The revelation of God resulted in a return of some of Ham’s descendants to submission to God. The calamity of judgment on the nation of Egypt held within it mercy—that those who did not descend from Abraham submitted to the God of Abraham the LORD.  Seeing the great and mighty power of God, their hearts became kindled to submit to him rather than their gods of Egypt or to Pharaoh.
I think this detail in Exodus 12:38 helps illuminate later issues in the wilderness, it adds to the complexity of the narrative. When we come to the whiners in the wilderness, rather than say, “Look at these ungrateful, sinning idiots,” we should see ourselves in them. This mixed multitude will not enter the Promised Land; however, the children of the mixed multitude will.
While we don’t wish to read more into this detail than we should, we absolutely must glean the significance from it. While these people sin in the wilderness, understand that they also leave their own land, people, language, and culture behind because of the revelation of God in judgment over them. Without knowing where they would go, they went with the people of Israel due to the acts of God among them.
Furthermore, the teaching of the Passover includes people like these. Exodus 12:48-49 state: But if a stranger sojourns with you, and celebrates the Passover to the LORD, let all his males be circumcised, and then let him come near to celebrate it; and he shall be like a native of the land. But no uncircumcised person may eat of it. The same law shall apply to the native as to the stranger who sojourns among you, (NASB, emphasis added). The alien who desires to submit to God in the way of worship he ordained does not remain alienated. He becomes like a a native.
As the New Testament points to the Passover’s true meaning in the revelation of Jesus Christ, we find that the Passover lamb will not deliver us, but Jesus will and does and has. If you repent of sin and believe in Christ, rejecting every false god you formerly served, worshiped, and praised, then you have become as a sojourner among the people of God who became as a native. Galatians 4 speaks of the Christian believer’s adoption into the family of God. No longer a slave, the Christian stands rooted as a member of the household of God. You were the Egyptian witnessing judgment on all that you knew and held dear, but you now have abandoned such things to be among the people of God by the work of God to adopt you into the family of God. Give him thanks and praise this day that you sit among the nations blessed by the offspring of Abraham in Jesus Christ.
W. Ross Blackburn, The God Who Makes Himself Known: The Missionary Heart of the Book of Exodus, vol. 28 of New Studies in Biblical Theology, ed. D. A. Carson (Downers Grove: InterVarsity Press, 2012), 50.