Exodus 12:51
And it came to pass the selfsame day, that the LORD did bring the children of Israel out of the land of Egypt by their armies. And it came to pass the selfsame day, that the LORD did bring the children of Israel out of the land of Egypt by their armies.
The selfsame day was the exact day on which the Lord brought the children of Israel out of the land of Egypt, completing the 400 years foretold to Abraham. The bringing out by armies means that Israel left Egypt in organized groups. The departure included carrying Joseph's bones, as a reminder of God's promise and their deliverance. It was a wonderful work in which God lifted Israel from long servitude and bondage by His mighty power, in a signal manner with a high hand and an outstretched arm, despite Pharaoh's opposition.
The deliverance came through multiplied signs and wonders that hardened Pharaoh because he would not receive them, with each rejected punishment bringing the next chastisement closer and more severe until his proud heart was humbled to acknowledge God. Those signs proved that the Maker of heaven and earth is the living and all-powerful God above all gods, whose strength is mightier than the strongest, against the feeble wisdom of Egypt's mighty men and the arrayed power of its gods. The same signs were for the advantage of God's people to give them clearer and more exalted views of God, so that all Israel would fear Him and be willing and anxious to leave Egypt and choose the service of the true and merciful God instead of remaining satisfied in Egypt rather than journeying through the wilderness.
God brought Israel out so the people could keep the law given in Eden, and He then brought them to Sinai to hear that law proclaimed. That bringing out, together with cutting a path through the waters of the sea and destroying Pharaoh's pursuing host, proved the hand that had safely guided them and meant He would certainly give them the land of Canaan He had declared He would give them. Israel should therefore have reflected on that deliverance, kept God in the question, and fully trusted His word to fulfill it instead of acting as though taking Jericho, the key to Canaan, must depend solely on power of arms. Forgetting it left God out, limited the work of God, and distrusted His guidance, and it produced bitter disappointment, wailing, reproach, blame of leaders, and murmuring against Moses and Aaron.