He speaks of this more directly in another epistle: "Do you not know that you are the temple of God, and that the Spirit of God dwells in you?" (1 Cor 3:16-17). The gathering of all Christians into the one spiritual temple of God’s glory shows their kinship with one another. It also shows their nearness to God, beyond which nothing greater can be imagined.
Together with the greatness of this spiritual image, its practical application is also very important. It stands over against the majestic Ephesian temple of the goddess Artemis, which did not elevate the spirit of its worshipers, but lowered it. They were full of enmity and every evil feeling.
According to the explanation of blessed Theophylact, the Apostle uses three comparisons to define the nearness of Christians to God. They are near as fellow citizens, as members of one family, and as parts of a building in relation to one another.
"We have become fellow citizens not simply of the Jews, but of men great in holiness, such as Abraham, Moses, and Elijah. See into what city we have been enrolled. See where we shall one day appear," says Saint John Chrysostom.
Elsewhere the Apostle says that the builder and maker of this city is God (Heb 11:10). "Believers have one Master, and wherever they live, all are fellow citizens" (Ambrosiaster).
"The thought of household members led to the thought of a house. In both the Old and the New Testament, the Church of God is presented under the image of a building, a house, or a temple. The Church is the temple of faith.
The Apostles are nearer to us and saw the truth tangibly. The prophets are farther away and saw the truth from afar, in images. Therefore the Apostles are placed first. The Apostles with the prophets, by the hand of preaching, take souls and peoples.
They place them into the building of the Church and join them to it. Thus stone is laid upon stone, and the building rises. The Apostles and prophets are laid as the foundation, and you complete the rest of the building" (Bishop Theophan).
"The Apostle added, ‘being the cornerstone,’ to show that Christ holds all things together. The cornerstone is what supports both the walls and the foundation, and on it the whole building is established. He bears all things upon Himself and holds all things together."
Whatever you point to, whether the roof, the walls, or anything else, He holds all things together and bears all things in Himself. "This temple, in which God dwells as in a body, is each one of you and all of you together."
Blessed Jerome writes: "If every building, fitly joined together, grows into a holy Church in the Lord, then we must spare no labor. We must strive to become living stones, hewn, cleansed, and polished on every side. Then we shall be built into a temple and shall be a dwelling for God."
In Bishop Theophan’s view, "everything that we believe about the Church is said here. She is one, being established on the one cornerstone. She is holy, being built by the Holy Spirit. She is catholic, embracing all times and peoples (14). She is apostolic, being built upon the foundation of the Apostles (20)."