The verse says, "you are petros [literally translated: a little stone] and upon this petra [literally translated: a huge boulder, big enough that you could build a house on it] I will build my church [called out] and the gates of hell will not prevail against it.

The only thing that can be solid is revelation.  Revelation that is true revelation always comes from God.  Most people don't realize that you cannot know anything at all without revelation.  https://seekfind.net/How_Can_We_Know_Anything.html  The only reason we know anything is because God reveals it to us.  Our natural minds always want to take credit for it, but all knowledge, understanding and wisdom comes from God.  In particular, Jesus was speaking of the revelation of Himself being this foundational Rock.  In Paul's first letter to the Corinthians, Paul says that there is no other foundation that can be laid other than Jesus Christ.  Paul also says, in Ephesians, that the apostles and prophets are the foundation of the Church with Jesus Christ being the chief corner stone.  The apostles are to walk in such submission to the Spirit of Christ that they become part of Him, the Foundation of the Church.  Another Scripture says, "If the foundations be removed, what shall the righteous do?"

This brings up the question, "What is the Church?"  The Church, the called out of God, the Temple of God, the Body of Christ or Christ the Body, the bride of Christ, is a specific thing.  It does not consist of the flesh natures of all the people who belong to an organization, but it consists of all the ministries (Christ in us) of the Christ-followers and the arrangement of those ministries into a holy Body that is built according to God's pattern (which is plainly shown in Scripture) and walking in submission to Christ the Head in Heaven to the point that these members are being changed into His same image from glory to glory by the Holy Ghost.  When the church has reached the completion of this process, that will be a fulfillment of what Scripture calls the manifestation of the sons of God or, as Ephesians has it: the unity... a perfect (totally complete) man... the measure of the stature of the fullness of Christ.  That will be Christ the groom joined in perfect and complete union with His spotless bride.