Isaiah 19:20

And it shall be for a sign and for a witness unto the Lord
of hosts in the land of Egypt
This refers either to what goes before, that the altar and pillar were signs and witnesses that the Lord was believed in, professed, and worshipped there; or to what follows after, that the Lord's hearing the cries of men, and answering them, by sending a great Saviour to them, is a token and testimony for him of his great love unto them:

for they shall cry unto the Lord because of the oppressors;
as men awakened and convinced do, feeling the oppressions of a guilty conscience, and a tempting devil, and an ensnaring wicked world:

and he shall send them a Saviour, and a great one, and he shall
deliver them;
this is Christ, whom God sent in the fulness of time to be the Saviour of lost sinners; and he is a "great" one indeed, the great God, and our Saviour, ( Titus 2:13 ) who is the Son of God, the true God, and eternal life, who has all the perfections of deity in him; the Creator and Upholder of all things; and must have therefore great and sufficient abilities to save sinners to the uttermost; and those that come to God by him he does save and deliver from all their sins, and out of the hands of all their enemies, and from wrath, ruin, and destruction. Abarbinel ^F5 owns that the Messiah is here meant, as undoubtedly he is; and not the angel that destroyed Sennacherib's army, as Kimchi; for the text speaks not of the Jews, but of the Egyptians. Vitringa thinks that either Alexander, called the Great, or else Ptolemy the son of Lagus, who had the same epithet, and who was also called "Soter", the saviour, is here meant.