# Scripture contains this

The scriptures are spoken of as if they were a container. This passage refers to the words that a person reads in scripture. Alternate translation: "This is what a prophet wrote in the scriptures long ago" 

# See

The word "see" here alerts us to pay attention to the surprising information that follows.

# a cornerstone, chosen and valuable

"a most important cornerstone, which I have chosen" 

# a cornerstone

The prophet speaks of the Messiah as the most important stone in a building.