What does it mean for Christ to be the church's cornerstone?

It is important to understand the nature of what Paul writes that we were dead in our sins and made alive in Jesus Christ, that we were formally Gentiles, not able to comprehend God and without hope.

By God’s grace and love through Jesus Christ and His death and resurrection, we are united with all believing Jews into one body. In Ephesians 2:20-21, Paul wants us to understand the glory of the church and what it means for Christ to be the church’s cornerstone, the same cornerstone as the one in Isaiah 28:16-17.

Jesus Christ is that costly cornerstone by which everything else is measured.