The church is the provisional representation of redeemed humanity.
Provisional because there are many currently on the outside who will be on the inside (and some on the inside who will be on the outside!) It is not good to speculate on the final make up of redeemed humanity. Provisional also because those on the inside are still sinners; they await the redemption of their bodies and their final revelation as God's children.
But still a representation. The church stands for the whole, acknowledging the work of Christ on its behalf - and on behalf of others. In the church it is known that Jesus Christ takes away sin - and not only the sin of the church but the whole world. The church knows that the day is coming when every knee will bow to Christ, and in its worship it anticipates and prefigures that day.
All of which has practical implications.
Because it is a representation of redeemed humanity, the church will be a disciplined community, seeking to live in holiness; because it is a provisional representation, the church will fall short and will need to show mercy to its members.
Because it is a representation of redeemed humanity, the church will have defined 'borders', acknowledging the unity of the one people of God; because it is a provisional representation, those borders will always be porous and open to all.
Because it is a representation of redeemed humanity, the church will clearly proclaim Christ, and the truth as it is in him; because it is a provisional representation, it will be always learning and forever repenting of its past misrepresentations of its Lord.
The church is a sign in the midst of the world that, in Christ, God has completely changed the situation of all human beings. The local church, by its very existence, is a sign that this is true of these particular human beings in this particular place. The task of the church is to seek more and more to conform its community life to the purpose of being this sign.