I grew up under the teaching that there could be and therefore indeed should be a pure church in this life. And there are parameters in scripture, both in teaching and in life that are to mark the true church. Indeed the church is called no less than God’s household and the pillar and foundation of the truth. Those who violate either orthodoxy (example: denial of Christ’s resurrection) or orthopraxy (example: living in unrepentant sexual immorality) are to be questioned and instructed and disciplined respectively – in love and then if they do not respond they are to be put out of the church and they become those who need to be evangelized.
Jesus’ parable of the wheat and the weeds (traditionally, tares) is interesting for this discussion. That seems to suggest that sometimes we can’t tell the difference between those who are genuine and those who are not in this world. So that we have to be careful. Applied to the church that might say we should go out of our way and bend over backwards not only to give time for repentance, but also to clear up misunderstandings on their part and perhaps on ours. But to remain faithful to scripture there does seem to come that time when lines are drawn. For example one who denies that Jesus is the only way to God should not think that they can be a “Sunday School teacher” even if they can teach quite well.
In the end, I’m not sure we’ll ever arrive in this life to a pure church. Strictly speaking we would all have to leave the church and then there would be nothing left. And we don’t want to discourage people from attending who may claim no faith at all and who may be overcome in sin.
But we also want to be those who affirm the truth of the gospel in our profession of faith and our life in this world. We are called to be faithful, to be the faithful ones in Christ Jesus. The confessing church in word and deed. And we must not forget that the church is called the bride of Christ no less, a bride he is preparing to be not only pure, but radiant in beauty. May the Lord help us all.