With a strong hand - A powerful hand; as by a hand that could grasp and subdue all that opposed.
And with a stretched-out arm - As if the arm were stretched out to strike with the utmost force, or to exert its utmost power. See Exodus 6:6; Deuteronomy 4:34; Deuteronomy 5:15; Deuteronomy 7:19; Deuteronomy 26:8; Jeremiah 32:21.
For his mercy - The exertion of his power in delivering his people was the expression of a mercy, the consequences of which are to endure forever, for the results of that deliverance will never cease in the history of the world; will never cease in heaven.

With a strong hand, and with a (d) stretched out arm: for his mercy [endureth] for ever.
(d) In doing such a work as was never done before, nor that any other could do.

With a strong hand, and with a stretched out arm,.... Exerting his power in a very open manner, and continuing it till he had effected the work; bringing his people out of Egypt, which is always ascribed to his great strength and mighty power, Exodus 13:3. The redemption of the mystical Israel of God is by a mighty Redeemer, the Lord of hosts; who has redeemed them out of the hands of their enemies, that were stronger than they, and too strong for them: the conversion of them is by the power of the grace of God, even by the exceeding greatness of his power, and yet both acts of grace and mercy;
for his mercy endureth for ever; it was mercy put the Lord on stretching out his arm, and showing the strength of his right hand, in delivering Israel out of Egypt; and in his love and in his pity he redeemed them, Isaiah 63:9. It is owing to the tender mercies of our God, and is a performing the mercy promised to the fathers, that Christ, the dayspring from on high, was sent to visit and redeem us, Luke 1:68; and the regeneration, quickening, and conversion of sinners, are acts of mercy as well as of power, Ephesians 2:4.

Compare similar expressions (Exodus 3:20; Deuteronomy 4:34, &c.).