Ambrose of Milan

Therefore, it is enough to mention the qualities and substance of the heavens that we find in the writings of Isaiah, who expressed the nature of the celestial sphere in ordinary and familiar language, saying that God has made the heavens firm like smoke, not wanting to reveal its subtle and immaterial nature. And he also speaks of its appearance, saying that God has made the heavens like a vault, within which all things in the sea and on land are enclosed. It is similarly signified when it is read: Because the Lord has stretched out the heavens. For it is extended like a skin to the dwellings and abodes of the saints; or like a book, so that the names of many who have deserved the grace of Christ by faith and devotion may be written, to whom it is said: Rejoice, because your names are written in heaven.