John Calvin Commentary Isaiah 54:12

"And I will make thy pinnacles of rubies, and thy gates of carbuncles, and all thy border of precious stones." — Isaiah 54:12 (ASV)

And I will lay thy windows with pearls. By these metaphors he shows that the condition of the Church, as has been previously said, will be far better than at any previous time. The Church is compared to a building, which is common throughout Scripture (Jeremiah 24:6; Matthew 16:18). For this reason he now draws a picture of a costly and magnificent structure. However, it should be noted that the Prophet represents God as the architect of this building, for this work should be entirely ascribed to him alone.

However, one may ask what the Prophet means by “carbuncles, sapphires, pearls,” and other kinds of jewels; for Paul used a similar metaphor to refer to doctrine. He says, As a wise architect, I have laid the foundation. And again,

If any man build on this foundation, gold, silver, precious stones, wood, hay, stubble, every man’s work shall be made manifest (1 Corinthians 3:10–13).

Whether or not this is the Prophet’s meaning will appear from the following verse.