The most important part of a building is the foundation. Without a solid and firm foundation, the structure would prove to be weak and unstable. The most important part of a foundation is the cornerstone (or setting stone). This stone is important because, as the first stone used in the construction of a foundation, all other stones are set in line with this stone. Thus, the angle, plumb and setting of the whole structure emanates from that one cornerstone.
In the spiritual realm, Jesus is the foundation and cornerstone of the church. As the Scripture says: For no other foundation can anyone lay than that which is laid, which is Jesus Christ (1 Cor 3:11). You are fellow citizens with the saints and members of the household of God, having been built on the foundation of the apostles and prophets, Jesus Christ Himself being the chief cornerstone (Eph 2:20). The chief or head cornerstone is fundamental and essential in the construction. It is placed between two walls in order to hold them together and keep the building from falling apart (see 1 Pet 2:4-7).
One of the reasons Jesus came to this earth was to build His church. After Peter had rightly confessed that Jesus was the Christ (Messiah, anointed one, deliverer), Jesus responded: And I also say to you that you are Peter, and on this rock (the solid confession that Jesus is the Christ), I will build My church . (Mt 16:18). What is not apparent in the English translation is the play on words in the Greek.
Peter is petros, a stone (see Jn 1:42 in the KJV & NKJV). This has reference to a piece of detached stone that one could easily pick up and throw. Rock is petra, meaning a mass of rock, rock ledge, or bedrock. This is the basis for a strong, solid and enduring foundation. And this is the Rock upon which the church of Christ is built.
For this reason, Jesus encourages you & me to build on the Rock. Therefore whoever hears these sayings of Mine, and does them, I will liken Him to a wise man who built his house on the rock: and the rain descended and the floods came, and the winds blew and beat on that house; and it did not fall, for it was founded on the rock (Mt 7:24-25). Now which Greek word do you suppose the Lord used here: petros or petra? When we obey the Lords teachings we are in effect building our spiritual house on the bedrock of Jesus Christ, a foundation that is strong solid and enduring.
The alternative is to build on the sand. This results in flimsy construction, permanent instability, and a tragic result. Now everyone who hears these sayings of Mine, and does not do them, will be like a foolish man who built his house on the sand: and the rain descended and the floods came, and the winds blew and beat on that house; and it fell. And great was its fall! (Mt 7:26-27).