1 Peter 2:5-6

5 you also, as living stones, are being built up as a spiritual house for a holy priesthood, to offer up spiritual sacrifices acceptable to God through Jesus Christ. 6 For this is contained in Scripture:

“BEHOLD, I LAY IN ZION A CHOICE STONE, A PRECIOUS CORNER stone,

AND HE WHO BELIEVES IN HIM WILL NOT BE DISAPPOINTED.”

We as believers are living stones. He is the cornerstone (the foundation stone) and we are all the other building stones, which are being built up as a spiritual house (metaphorically). We are built up for a holy priesthood (v. 9)—each of us being priests of God, working in the service of God and having access to God. As priest we offer up our bodies as a living sacrifice for all the work He would have us do for Him (Rom. 12:1).

Verse 6 is a quote from Isaiah 28:16. It is a prophecy of the Messiah to come, and all who believe in Him will not be disappointed; that is, He will be all that He has been prophesied to be and all that we need Him to be.