Charles Ellicott Commentary Isaiah 19:21

"And Jehovah shall be known to Egypt, and the Egyptians shall know Jehovah in that day; yea, they shall worship with sacrifice and oblation, and shall vow a vow unto Jehovah, and shall perform it." — Isaiah 19:21 (ASV)

The Egyptians shall know the Lord ... —Here also we note what we may venture to call the catholicity of Isaiah’s mind. The highest of all blessings, the knowledge of God as He is (John 17:3), was not to be the exclusive inheritance of Israel, but was to be shared even by the nation whom she had reason to regard as her hereditary enemy.

Sacrifice and oblation. —The two words describe respectively the slain victims and the meat, or rather, meal, offerings of the Law. Did the prophet, we ask, think of such sacrifices as literally offered in Egypt, or did he look beyond the symbol to the thing symbolized? The builders of the temple at Leontopolis took the former view. Those who have entered into the mind and spirit of Isaiah will be inclined, perhaps, to take the latter. A literal fulfillment has been found in the fact that Ptolemy Euergetes (B.C. 244) came to Jerusalem to offer sacrifices in the Temple.