Isaiah 19:21

And the Lord shall be known to Egypt - Shall be worshipped and honored by the Jews who shall dwell there, and by those who shall be proselyted to their religion.

And the Egyptians shall know the Lord - That many of the Egyptians would be converted to the Jewish religion there can be no doubt. This was the result in all countries where the Jews had a residence (compare the notes at Acts 2:9).

And shall do sacrifice - Shall offer sacrifices to Yahweh. They would naturally go to Jerusalem as often as practicable, and unite with the Jews there, in the customary rites of their religion.

And oblations - The word מנחה minichāh ‘oblation,’ denotes any offering that is not a “bloody” sacrifice - a thank-offering; an offering of incense, flour, grain, etc. (see the notes at Isaiah 1:13) The sense is, that they should be true worshippers of God.

They shall vow a vow ... - They shall be sincere and true worshippers of God. The large numbers of the Jews that dwelt there; the fact that many of them doubtless were sincere; the circumstances recorded Acts 2:9, that Jews were in Jerusalem on the day of Pentecost; and the fact that the true religion was carried to Egypt, and the Christian religion established there, all show how fully this prediction was fulfilled.