The unity of the Spirit.
Eph 4:3 NET
There is one body and one Spirit.—Through him we both have access in one Spirit to the Father. So then you are no longer foreigners and noncitizens, but you are fellow citizens with the saints and members of God’s household, because you have been built on the foundation of the apostles and prophets, with Christ Jesus himself as the cornerstone. In him the whole building, being joined together, grows into a holy temple in the Lord, in whom you also are being built together into a dwelling place of God in the Spirit.
Look! How good and how pleasant it is when brothers live together! It is like fine oil poured on the head which flows down the beard – Aaron’s beard, and then flows down his garments.
You have purified your souls by obeying the truth in order to show sincere mutual love. So love one another earnestly from a pure heart.
Eph 4:4, Eph 2:18-22, Ps 133:1-2, 1 Pet 1:22