These verses include three quotations from the Old Testament. Each one describes Christ as a kind of stone:
The first quotation calls him the cornerstone on which God builds the new temple (2:6).
The second quotation calls him the cornerstone that people rejected, but God raised up to become the most important stone in his plan to save the world (2:7).
The third quotation calls him the stone that makes people stumble when they refuse to believe (2:8).
Jesus quotes Psalm 118:22 in Matthew 21:42. Paul quotes both Isaiah 8:14 and 28:16 in Romans 9:33. These three Old Testament passages were likely brought together very early in the church. Early believers probably used them as a combined witness to the identity and importance of Jesus the Messiah.