The true Church was built by Jesus Christ on Peter. " And I tell you, you are Peter (rock), and on this rock I will build my church, and the powers of death shall not prevail against it."
Peter is nothing.
In bible times, building were constructed of stone. The cornerstone, was in those times the most important stone. It was the most carefully constructed stone, and if it was in any way, out of plumb or alignment no matter how minor; it was rejected by the builders. Once the cornerstone was set, it became the basis for determining every measurement in the remaining construction; everything was aligned to it. As the cornerstone of the building of the church, Jesus and His written word is our standard of measure and alignment.
Isaiah in the OT prophesied about Jesus being the cornerstone.
Isaiah 28:16-17
So this is what the Sovereign Lord says:
“See, I lay a stone in Zion, a tested stone,
a precious cornerstone for a sure foundation;
the one who relies on it
will never be stricken with panic.
17 I will make justice the measuring line
and righteousness the plumb line;
hail will sweep away your refuge, the lie,
and water will overflow your hiding place.
Jesus quoted it
Matthew 21:42
Jesus said to them, “Have you never read in the Scriptures: ‘The stone the builders rejected has become the cornerstone; the Lord has done this, and it is marvelous in our eyes’?
Jesus is the firm foundation for our lives, if all would but trust in Him. The Rcc has built upon peter, which is something different from what God is building upon.