Isaiah 19:18-25 presents a bizarre look at “that day” when even some people from God’s notorious enemy nations will be saved.  Israel’s problem in Isaiah has been the tendency to trust the nation, Assyria, for help (cf. also 2 Kings 16:7).  In vv. 18-22 Isaiah shows us what will happen to some individuals because of God’s activity.  Verse 21 shows what they will do and their actions become an example for every Believer to follow.  Also important for the Church is to be sure that we will be in this trio of blessed people: Egypt, Assyria, and Israel.  Of course, that requires that we are working now with God in making Himself known to the nations.  It’s His mission; it’s our mission.  Remember that prophetic Texts are designed to drive us toward more holiness and faithfulness.  This picture of God’s future day is a day we participate in partially now because of Christ’s accomplishments.  It’s not just will Christians be in on that day, but how are we participating in part of that day now through faith in Christ.  This angle fits many Old and New Testament prophetic and visionary Texts.