Peter is a stone, just as we are.

The rock is Christ, the chief cornerstone.

I'll let Peter tell you himself.

1 Peter 2:1-10

1 Wherefore laying aside all malice, and all guile, and hypocrisies, and envies, and all evil speakings,

2 As newborn babes, desire the sincere milk of the word, that ye may grow thereby:

3 If so be ye have tasted that the Lord is gracious.

4 To whom coming, as unto a living stone, disallowed indeed of men, but chosen of God, and precious,

5 Ye also, as lively stones, are built up a spiritual house, an holy priesthood, to offer up spiritual sacrifices, acceptable to God by Jesus Christ.

6 Wherefore also it is contained in the scripture, Behold, I lay in Sion a chief corner stone, elect, precious: and he that believeth on him shall not be confounded.

7 Unto you therefore which believe he is precious: but unto them which be disobedient, the stone which the builders disallowed, the same is made the head of the corner,

8 And a stone of stumbling, and a rock of offence, even to them which stumble at the word, being disobedient: whereunto also they were appointed.

9 But ye are a chosen generation, a royal priesthood, an holy nation, a peculiar people; that ye should shew forth the praises of him who hath called you out of darkness into his marvellous light;

10 Which in time past were not a people, but are now the people of God: which had not obtained mercy, but now have obtained mercy.

Worth noting the Rockefellers, who purchased the Encyclopedia Britannica, have even corrupted the meaning of cornerstone (and openly admit as much)-

Until the development of modern construction, the stone was usually at a corner, possibly as the first of the foundation stones, and it was a real support. The modern cornerstone need not actually support, need not be positioned at a corner, and need not be part of the foundation; often it is placed ornamentally in the facade or in an interior wall or floor.

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