adding back JM's image addition
The word "Church" arises in Christian use from a number of New |Testament sources, perhaps the prime, the words of Jesus - "On this rock I will build by Church". This is at once concrete and it is general with portents of the future. It is concrete as Church, the "Ekkelsia" those that are "called out" (of the environs) for the purpose of gathering together is a direct reference to the synagogue ("led or assembled togther") - "Beit Knesset" in Hebrew, those that are "gathered together", visible, concrete, societal, a people. These then, together are the Israel of God, a new creation, upon which will sit, guide, judge, the 12 apostles, waiting for the Lord to return.
And yet, Church, is something beyond this, something that takes it in but transcends this as Church is somehow related to the Body of the Risen Christ which He now in Heaven fills and lives in here on earth. We the Church have now somehow by His grace become part of His Body, or we ,all together, are His Body on earth, through which He lives and continues His good and continuing work of the Kingdom of God.