Isaiah 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.
Cross-reference
Isaiah 19:18
Parallel
Isaiah 19:18 describes Egyptian cities swearing allegiance—this verse adds the altar and pillar as tangible signs of that worship.
Isaiah 66:23
Parallel
Isaiah 66:23 expands the vision: all nations worship — the altar in Egypt becomes part of universal worship.
Exodus 24:4
Allusion
Exodus 24:4 records Moses building an altar and twelve pillars — the same two elements together, suggesting a covenant memorial pattern.
Hosea 3:4
Contrast
Hosea 3:4 says Israel will be without a pillar, contrasting with Egypt having one—a reversal of worship symbols.