Why are we called "OIKOU" ?   ... a spiritual household, and environment...

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OIKOU, Greek: house, household affairs [environment, habitat], home, dwelling; used in one extensive sense as, "environment"
 ... a spiritual household, and environment...

Morphology of Biblical Greek term oikou : 

Gloss:
house, home, a physical edifice; of royalty: palace; of deity: temple; by extension: family, lineage, people who live in or originated in a particular house, a land or nation, the environment

Oikou Biblical Definition: 
a house, dwelling, Mt. 9:6, 7; Mk. 2:1, 11; 3:20; 
place of abode, seat, site, Mt. 23:38; Lk. 13:35;
met. a spiritual house or structure, 1 Pet. 2:5;
meton. a household, family, Lk. 10:5; 11:17; 
a spiritual household, 1 Tim. 3:15; Heb. 3:6; 
family, lineage, Lk. 1:27, 69; 2:4;
from the Hebrew, a people, nation, Mt. 10:6; 15:24

Oikou Liturgical Reference: 
There are countless references in the liturgical life of the church. Here is a tiny example
... υπερ το αγιο οικου τουτο
... Υπέρ του αγίου οίκου τούτου και των μετά πίστεως, ευλαβείας και φόβου
...  Ένεκα του οίκου τού Κυρίου τού Θεού μας
... ο άναξ, ο κύριος οίκου, οικοδεσπότης

The ancient Greek word
Oikos (ancient Greek: οἶκος, plural: οἶκοι; English prefix: eco- for ecology and economics) refers to three related but distinct concepts: the family, the family's property, and the house.

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