"In Him" means in the cornerstone, who is Jesus Christ, for in the Church everything is from Him, according to His plan, by His power and action. "Every building" more directly means the whole building as one whole, for the Apostle speaks of one building, not of many constructions.
"Being fitly joined together" means being harmonized. The materials that enter are not thrown in at random, but are set in place according to one plan. The building comes forth in good order, with each thing in its own place. "This points to the care, attention, and fidelity to the plan of the construction" (Oecumenius).
It also points to the different parts of the building, all of which are joined into one in the same cornerstone, Jesus Christ. "Whatever you point to, whether the roof, the walls, or anything else, He holds all things together and bears all things upon Himself" (Saint Chrysostom).
This is the same thing he says below without metaphor: "And He gave some to be Apostles, some prophets, some pastors and teachers, for the perfecting of the saints, for the building up of the body of Christ" (Eph 4:11).
Elsewhere the Apostle also distributes the saints, that is, the believers who make up the body of the building, as the various organs of the body are distributed among us. Each member has its own significance and its own work.
In the Church of God everything is harmonized, but she is diverse in her parts. It is impossible to say that in her all are as one, and each is as all. Where all are identical and equal, what harmony can there be?
Only under this condition, that the members in the Church are different and are brought into harmony, does she grow. She grows by being formed in ordered harmony. At first raw material enters, which in its natural condition is not fit for the building.
Therefore it is first remade and brought under the character of the building, and only then is it placed in the building itself. Through these additions the building grows. Individuals and whole peoples, called by preaching, are transformed by the grace of the Holy Spirit and thus are merged into the wholeness of the Church.
"It grows." In the time of the Apostles they said, "It grows." To this day one can speak no otherwise than, "It grows." Until the end of the age she will grow. The building is not yet finished. It will be finished at the end of the ages.
Those who have departed into the other life are in the Church, and those who live are in the Church. The Apostle does not set a division between them. The Church is one.
One may imagine only this: the earthly Church prepares the material, while the building itself, in its finished form, is built in heaven. Hermas saw the construction of a temple in a vision. Some brought material, while others built.
The builders received what was brought and examined whether it was suitable and where it was suitable. If it was suitable, they placed it in its proper place. If it was unsuitable, they threw it away. Though it lay nearby, it did not enter the building.
This is an exact image of what happens to those who depart from here. When the building is finished, all those stones lying around will be removed to another place. Until then, they are still nearby. Their lot has not been decided.
It grows into a holy church, into a holy temple. Everything tends toward this: that at last God may be all in all. But until then, is the Church not a whole building, lacking roof, windows, and doors? How can one dwell in such a building?
Yet God dwells in the Church, as He promised: "I will dwell in them and walk among them" (2 Cor 6:16). For this reason the Apostle used the word "grows," presenting the Church as a living building. She already has everything necessary for her existence and life.
A tree, for example, even when still very small, has everything necessary for life. Later it grows, not by acquiring new parts, but by increasing and expanding in each part it already has. So the Church now is a whole and habitable building, but she increases until she reaches the measure of the temple as God conceived it.
The Church is a holy temple because all her members are holy, sanctified by the Holy Spirit, and zealous to be holy. She is also holy because the Holy God dwells in her.
"In the Lord": the temple is holy in the Lord, it grows in the Lord, and it is harmoniously joined in the Lord. In the Church everything, whatever you take, is in the Lord, as Saint Chrysostom said. Saint Paul also said at the beginning, "in Him," meaning the Lord, and at the end he added "in the Lord," so that our attention might remain fixed upon Him alone.
However beautiful the temple building may be, do not become absorbed in looking at it and forget the builder of the temple. For this reason he does not enlarge here on explaining the details of the temple’s construction.
His aim is to impress upon the Ephesians that they too are included in the common building, and for no other reason than faith in the Lord and fidelity to Him. They too have been brought near to all, but in the Lord.