Let’s begin by reading the prophesy to which you refer. In Isaiah 19:20-25 we read, “And it shall be for a sign and for a witness unto the LORD of hosts in the land of Egypt: for they shall cry unto the LORD because of the oppressors, and He shall send them a saviour, and a great one, and he shall deliver them. 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 smite Egypt: He shall smite and heal it: and they shall return even to the LORD, and He shall be intreated of them, and shall heal them. In that day shall there be a highway out of Egypt to Assyria, and the Assyrian shall come into Egypt, and the Egyptian into Assyria, and the Egyptians shall serve with the Assyrians. In that day shall Israel be the third with Egypt and with Assyria, even a blessing in the midst of the land: Whom the LORD of hosts shall bless, saying, Blessed be EGYPT MY PEOPLE, and Assyria the work of My hands, and Israel Mine inheritance”.

You’ll notice the use of the phrase “in that day” repeated several times in the verses above, and thus, we see, the complete fulfillment of this prophesy relates to the end times, when the Lord Jesus returns to this earth, and the enemies of Christ are defeated along with the beast and the anti-Christ. In that day, once the judgments of the nations during the tribulation are completed (see Revelation 14-19, the faithful of Israel, those who accepted Christ as their Lord, will be blessed in their land, and Jerusalem will be the seat of Christ’s government, and the center of blessing for all the nations who in that day accept Christ Jesus as Lord and king. So, this prophesy points to the millennial reign of Christ whereby  the faithful of all the nations will be blessed. In that day, the historical enemies of Israel, the Egyptians and the Assyrians, will have a special alliance with Israel, and Israel will be the center of worship. Thus, in that day, Egypt can indeed be called by God “Egypt My people” since they will have returned to the true God.  Now, I’m not sure if or just how this might fit in to this prophesy in Isaiah 19, but it is worth noting that twice in the history of Egypt, God used Egypt to protect and care for His people (God sheltered the patriarch Jacob and his family in Egypt that they might be saved from famine under the care of Jacob’s son Joseph after Joseph had been sold into slavery in Egypt, and after Joseph had risen to the second leadership position under the Pharaoh in Genesis 45-50; see also Matthew 2:13-15 where God called upon Joseph, Mary’s husband, to take the Christ-child to Egypt to avoid Herod’s plot to kill Him). Again, I’m not sure exactly how these two accounts fit in, except to say that God used Egypt on two occasions to care for Israel and the Christ, and thus, Egypt did not always play the role of enemy.

Now, we also read in Revelation 21 that ultimately, the faithful of all the nations of the world (including the former enemies of Israel) will be blessed “And the nations of them which are saved shall walk in the light of it: and the kings of the earth do bring their glory and honour into it,” (verse 24). So, in Revelation we do see that in that latter day when Christ shall rule that Jerusalem will be the center of worship for all the faithful of the nations of the earth, and this includes Egypt.

In conclusion, I’d like to quote a few paragraphs from the MacDonald Bible Commentary on Isaiah 19: “The first fifteen verses have already been fulfilled. Following the death of Tirhakah, who was ruling Egypt at the time of Isaiah’s prophecy, the country was torn by civil strife. Egypt was split up into twelve kingdoms, all subject to Assyria. Finally, the country was united again under Psammetichus, the “cruel master” of verse 4. The rest of the chapter is still unfulfilled….

  • Isaiah 19:18-29 – But the land of Egypt is promised restoration also. Five cities will become centers for the worship of Jehovah, including Heliopolis (city of the Sun), also called the City of Destruction. There will be an altar to the Lord in the midst of the land, and a pillar to the Lord at its border, both of which will be witnesses to the Lord. Josephus tells us that the prophecy of verse 19 was fulfilled in 1 b.c. when Onias, the high priest, fleeing from Jerusalem, obtained permission to build an altar in Egypt. But the full meaning of the prophecy is undoubtedly millennial.
  • 19:21-22 – God’s judgments on Egypt will succeed in bringing the people to worship Him.
  • 19:23 – A highway will pass from Egypt (through Israel) to Assyria with unrestricted passage. The nations will unite in the worship of Jehovah.
  • 19:24-25 – Then Israel will be one of three with Egypt and Assyria, that is, they will form a triple alliance, enjoying the blessings of Christ’s kingdom…”.  (SF)  (514.4)