"But if I am delayed, I write so that you may know how you ought to conduct yourself in the house of God, which is the church of the living God, the pillar and ground of the truth."
By knowing how to live in "the house of God," we then know how to live everywhere else: in our own houses, in culture, etc. But how will we know how to live in the church, without the word of God itself, which instructs us to do so?
The church, as "the pillar and ground of the truth," holds out the word to us, so that we may hear it (and read it). It is only in the context of the family of God, that we may know how to live as the children of grace.
[Puritan quote of the day: "You cannot know the love of Christ, before you know the badness of your nature." --John Bunyan, in "All Loves Excelling"]