What does Ephesians 2:21 mean?

Believers are part of this structure (Ephesians 2:20), the church, which exists as a holy temple in the Lord. Jesus is the cornerstone, the apostles and prophets are the foundations, and other believers are the additional parts (Ephesians 2:22) that make up this figurative temple that worships God.

In 1 Corinthians 6:19–20, Paul also refers to each believer's body as a temple. Though this is a slightly different word picture, the idea is relevant to this context. We must each see ourselves as a temple of God and live a holy life. In addition, we each serve as part of a holy temple that includes all other believers. We are to seek to live pure as a church body to be pleasing to God in our worship. Both aspects are of great importance to God. As with the Old Testament, the temple could become defiled and needed to be cleansed. Believers likewise need to confess sins (1 John 1:8–9) and be united as a body to live in a way that is pleasing to God.