Mark 12:10

And have ye not read this scripture; The stone which the builders rejected is become the head of the corner:

The saying about the stone the builders rejected becoming the head of the corner belongs to the parable of the vineyard, spoken as part of Jesus' final warning at the temple where He acted as Israel's king and gave evidence of His divine mission.
The stone is Christ, who was rejected and then made the head of the corner, the cornerstone and the chief cornerstone.
Rejected by men, He was exalted to be the chief cornerstone of God's building.

The builders are the Jewish leaders who rejected Christ, and their treatment of Him fulfills the image of the rejected stone.
Christ Himself, not Peter, is the rock and foundation on which the Christian church is built.
The word Peter signifies a loose stone, showing that by the rock Christ meant Himself and not Peter.

The exaltation of the rejected stone as the cornerstone is the Lord's doing and is marvelous.
It is the same stone described as the sure foundation and precious cornerstone in Isaiah 28:16 and as the stone in Luke 20:17-18.
In the vineyard parable the Jewish nation's contemptuous and cruel treatment of God's messengers would bring punishment and the transfer of the vineyard to other husbandmen who would render its fruits.

By rejecting Christ and working to turn the nation against Him, the leaders made themselves responsible for the nation's sin and ruin.
The vineyard parable applies not only to the Jewish nation but also to the church in the present generation.
That church has received great privileges and blessings from God and is expected to return fruit accordingly.