Chief Cornerstone

This is one of the names for God that is not completely understood. In the natural world a cornerstone is a large chunk of rock or masonry, like a concrete form. These are quite frequently hollow with a time capsule enclosed. The time capsule holds a treasure that needs to be remembered saying this is who we were and what we were all about. The question arises how could Jesus have been a physical thing rather than a being.

Is 28:16 Therefore thus says the Lord GOD:
"Behold, I lay in Zion a stone for a foundation,
A tried stone, a precious cornerstone, a sure foundation;
Whoever believes will not act hastily.

Jesus was a very special stone placed in Zion through the womb of a young woman, first presented in a stable. As 1 Peter 2:4-10 calls him a living stone, us as well.

1 Peter 2:4 -7, 9- 10 God said 4Coming to Him as to a living stone, rejected indeed by men, but chosen by God and precious, 5you also, as living stones, are being built up a spiritual house, a holy priesthood, to offer up spiritual sacrifices acceptable to God through Jesus Christ. 6Therefore it is also contained in the Scripture, "Behold, I lay in Zion A chief cornerstone, elect, precious, And he who believes on Him will by no means be put to shame." (NKJV)

I once had a pastor was preaching about believers being living stones and how some were moving from church to church. I drew a cinder block with a face, legs, and arms that was running away from the building the was placed in.

(1Peter 4:7) Therefore, to you who believe, He is precious; but to those who are disobedient, "The stone which the builders rejected Has become the chief cornerstone," (8) and "A stone of stumbling And a rock of offense."

Is 8:14 He will be as a sanctuary,
But a stone of stumbling and a rock of offense
To both the houses of Israel,
As a trap and a snare to the inhabitants of Jerusalem.

The old testament was a precursor of the new. You need to bear in mind there was nearly a 500 year separation between Isaiah and Peter. Isaiah predicted far in the future Peter confirmed what had happened.

1Peter 4: 9But you are a chosen generation, a royal priesthood, a holy nation, His own special people, that you may proclaim the praises of Him who called you out of darkness into His marvelous light; 10who once were not a people but are now the people of God, who had not obtained mercy but now have obtained mercy.

Since Peter was trying to impart knowledge and relationship with the risen Savior to the new Christians. I would imagine Isaiah had only the dimmest notion of what he was predicating.

Before lambs bled in Egypt, One was given.
Before the worm tore Eden, pain was faced.
Somewhere, before earth’s cornerstone was placed,
a hammer crashed in heaven—nails were driven.
Keith Patman (Draper’s book of quotations for the Christian World)

In (All the Divine Names and Titles in the Bible by Herbert Lockyer) there is a very interesting turn of the phrase.

Peter not only describes Christ as "A living stone," (1 Peter 2:4, 6), but those redeemed by His blood as "lively stones" (1 Peter 2:5). They are as "chips off the old block" as it were, partaking of His appearance and character."

A cornerstone is important. It is called corner because it forms part of a corner or angle in a wall, and is usually laid at the formal inauguration of a building. No building is considered complete until it has this important signature of the building.

Zech 4:7 ‘Who are you, O great mountain? Before Zerubbabel you shall become a plain! And he shall bring forth the capstone With shouts of "Grace, grace to it!"’"

The divine Builder brings His pattern from heaven and builds according to His own image.
(All the Divine Names and Titles in the Bible by Herbert Lockyer)

This has little to do with the cornerstone except for the fact that to this is often where important documents are preserved.

…archaeology throws interesting light on the possible reason for the repairmen’s finding this document in their work on the temple. The discovery is closely linked with the activity of the stonemasons and carpenters, and it is entirely possible this copy of the Pentateuch had been placed in the cornerstone of the temple when it was erected by Solomon (c. 966 b.c.). Doubtless the masonry documents come to light. Archaeology has demonstrated that it was customary in ancient times to place documents in the foundations of buildings, as it is done even to the present day. (Willmington’s Guide to the Bible)

Life Application Bible puts it this way:

Although Jesus had been rejected and defeated by his own people, the Jews, God would raise him from the dead and seat him at his own right hand. Nothing can thwart God’s purpose.
They wanted a political king, not a spiritual one. Yet God’s plans will not be thwarted. One day that rejected stone will indeed become the "cornerstone" with all the right qualifications—for Jesus will come as King to inaugurate an unending kingdom. And he had already begun a spiritual kingdom as the cornerstone of a brand-new "building," the Christian church.
The "rock" refers to Jesus himself (his work of salvation by dying for us on the cross). This would mean that Jesus is the divine architect of our faith and that he himself is the chief cornerstone.

Biblical Theology of the New Testament tells us about Cornerstones and capstones

They were valued architectural pieces. Stone masons demonstrated their ability by choosing just the right rock. Cornerstones anchored and shaped the foundation of a large building. They had to be square and solid. Capstones required a special shape. They were the final piece in an arch. Jesus is both cornerstone and capstone. Jesus’ role gives shape to all of history.

I am sorry I had to spent so much time quoting from the reference books but my knowledge doesn’t hold a candle to the scholars of the ages.