He sent a man before them, even Joseph, who was sold for a servant:

Jamieson-Fausset-Brown Bible Commentary

17-21. Joseph was sent of God (Ge 45:5).

Matthew Henry's Concise Commentary

105:8-23 Let us remember the Redeemer's marvellous works, his wonders, and the judgments of his mouth. Though true Christians are few number, strangers and pilgrims upon earth, yet a far better inheritance than Canaan is made sure to them by the covenant of God; and if we have the anointing of the Holy Spirit, none can do us any harm. Afflictions are among our mercies. They prove our faith and love, they humble our pride, they wean us from the world, and quicken our prayers. Bread is the staff which supports life; when that staff is broken, the body fails and sinks to the earth. The word of God is the staff of spiritual life, the food and support of the soul: the sorest judgment is a famine of hearing the word of the Lord. Such a famine was sore in all lands when Christ appeared in the flesh; whose coming, and the blessed effect of it, are shadowed forth in the history of Joseph. At the appointed time Christ was exalted as Mediator; all the treasures of grace and salvation are at his disposal, perishing sinners come to him, and are relieved by him.