Sing unto the Lord - This is the same expression which occurs in the song of Moses Exodus 15:21. Isaiah evidently had that in his eye.
He hath done excellent things - Things that are exalted (גאות gê'ûth); that are worthy to be celebrated, and had in remembrance; things that are majestic, grand, and wonderful.
This is known in all the earth - Or, more properly, ‘Let this be known in all the earth.’ It is worthy of being celebrated everywhere. It should be sounded abroad through all lands. This expresses the sincere desire of all who are redeemed, and who are made sensible of the goodness and mercy of God the Saviour. The instinctive and the unceasing wish is, that the wonders of the plan of redeeming mercy should be everywhere known among the nations, and that all flesh should see the salvation of our God.