“If we are not willing to admit a church unless it be perfect in every respect, we leave no church at all. True, indeed, is Paul’s statement:
‘Christ … gave himself up for the church that he might sanctify her; he cleansed her by the washing of water in the word of life, that he might present her to himself as his glorious bride, without spot or wrinkle,’ [Eph. 5:25–27].
Yet it also is no less true that the Lord is daily at work in smoothing out wrinkles and cleansing spots. From this it follows that the church’s holiness is not yet complete.
The church is holy, then, in the sense that it is daily advancing and is not yet perfect: it makes progress from day to day but has not yet reached its goal of holiness.”
–John Calvin, Institutes of the Christian Religion, ed. John T. McNeill, trans. Ford Lewis Battles, vol. 1, The Library of Christian Classics (Louisville, KY: Westminster John Knox Press, 2011), IV.i.17; p. 1031.