In the Coptic Church, this boundary is part of the architecture of worship. It teaches reverence while surrounding the altar with the confession of the Incarnation and the witness of the saints.
Veil, icons, and Incarnation
The Old Testament type is the veil of the tabernacle and temple, which marked holy space and guarded the approach to the Holy of Holies. The people learned reverence through visible boundaries.
The icon side of the question also has a biblical root in the reality that God works through visible signs. In Christ, the invisible God is revealed in the flesh, and the Church confesses that reality through holy images.
By a new and living way which He consecrated for us, through the veil, that is, His flesh.
Christ fulfills the veil by opening the way to the Father through His flesh, Cross, and Resurrection. The Coptic curtain does not close Christ away from the people.
How it works in worship
In many Coptic churches, the iconostasis stands between the nave and sanctuary, with doors or curtains used in the service. Icons are arranged to teach the faith and surround the altar with the witness of the saints.
The priest and deacons pass through the doors according to the rite. The opening and closing of the curtain can focus attention on prayer, preparation, and the solemnity of the Eucharistic service.
The curtain and iconostasis teach reverence for the mystery being served and show that the Church worships with heaven: angels, saints, martyrs, the Theotokos, and the whole Body of Christ gathered around the Lamb.
How to read it
When you see the iconostasis, read it as theology in wood, icons, doors, and curtains. It says that worship is holy, Christ is incarnate, and the saints worship with us.
If the boundary feels unfamiliar, let it slow you down rather than frustrate you. The Church often teaches through reverent limits before she explains them in words.