Albert Barnes Commentary Isaiah 10:21

"A remnant shall return, [even] the remnant of Jacob, unto the mighty God." — Isaiah 10:21 (ASV)

The remnant ... — That is, those who will be left after the invasion of Sennacherib.

Shall return — Will abandon their idolatrous rites and places of worship, and will worship the true God.

The mighty God — The God that had demonstrated his power in overcoming and destroying the armies of Sennacherib.