John Gill Commentary Psalms 136:12

"With a strong hand, and with an outstretched arm; For his lovingkindness [endureth] for ever:" — Psalms 136:12 (ASV)

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 13:3Exodus 13:9) (Exodus 15:6Exodus 15:16) (Exodus 32:11) . 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 1:68Luke 1:72Luke 1:78) ; and the regeneration, quickening, and conversion of sinners, are acts of mercy as well as of power, (Ephesians 2:4Ephesians 2:5) (1 Peter 1:3) .