An altar for God's worship; not a Levitical, but a spiritual and evangelical altar, as appears from hence, because that was confined to one place, Deuteronomy 12:13,14. The altar is put for the worship of God, as it is in many places both of the Old and New Testament. And nothing is more common in the prophets than to speak of gospel worship in the phrases of the law. A pillar; a monument of the true religion. Here also he alludes to the ancient custom of erecting pillars to God; of which See Poole on "Genesis 12:7", See Poole on "Genesis 28:18", See Poole on "Joshua 22:10", See Poole on "Joshua 24:26", See Poole on "Joshua 24:27". At the border thereof; as before, in the midst of it. The meaning is, There shall be evidences of their piety in all places.
Related Commentaries of Isaiah 19:19
Isaiah 19:19
19 In that day shall there be an altar to the LORD in the midst of the land of Egypt, and a pillar at the border thereof to the LORD.