Isaiah 19:21
And the LORD shall be known to Egypt, and the Egyptians shall know the LORD in that day, and shall do sacrifice and oblation; yea, they shall vow a vow unto the LORD, and perform it. And the LORD shall be known to Egypt, and the Egyptians shall know the LORD in that day, and shall do sacrifice and oblation; yea, they shall vow a vow unto the LORD, and perform it.
Isaiah 19 is a prophecy concerning Egypt, a great part of which has already been fulfilled in Egypt centuries ago rather than in modern times. It promises that Egypt will come to know the Lord, recognizing Him and responding with worship, sacrifice and oblation, and with vows that are performed.
That knowing the Lord includes renouncing idolatry, proved by the cutting off of idols, so that for three hundred years neither the nominal Christians of Egypt nor the Muslim inhabitants allow images to appear among them. This knowledge came to Egypt through its distress and downfall and through the spread of God's truth there.
In Egypt the knowledge of God was expressed in a center of devotion and worship represented by the altar and in the growth of strong Christian churches. The verse foretells the preaching of the gospel in Egypt and Assyria in New Testament times, illustrated by devout men from Egypt being present at Pentecost and by the treasurer of Candace carrying the good news of the Saviour south of Egypt. It encourages the expectation that Egypt will receive a witness to Jehovah and learn of the Saviour who delivers from the oppression of sin, with a fuller manifestation in the near future when the light of the third angel's message shines in Egypt.