Adam Clarke on Acts 13:17

The God of - our fathers - The apostle begins his discourse with the Egyptian bondage, and their deliverance from it, as points the most remarkable and striking in their history; in which the providence and mighty power of God, exerted so frequently in their behalf, were peculiarly conspicuous.

Exalted the people - Even when they were strangers in the land, and greatly oppressed, God exalted them; made them a terror to their enemies, and multiplied them greatly.

With a high arm - A literal translation of the Hebrew phrase, בזרוע רמה bezeroa ramah, with a lifted-up arm, to protect them and destroy their enemies. The meaning of the phrase is, a manifest display of the Divine power.