The passage concerning the perfection of the church is most likely Ephesians 5: 24-33 which reads as follows:
“As the church is subject to Christ, so let wives also be subject in everything to their husbands. Husbands, love your wives, as Christ loved the church and gave himself up for her, that he might sanctify her, having cleansed her by the washing of water with the word, that he might present the church to himself in splendor, without spot or wrinkle or any such thing, that she might be holy and without blemish. Even so husbands should love their wives as their own bodies. He who loves his wife loves himself. For no man ever hates his own flesh, but nourishes and cherishes it, as Christ does the church, because we are members of his body. “For this reason a man shall leave his father and mother and be joined to his wife, and the two shall become one flesh.” This mystery is a profound one, and I am saying that it refers to Christ and the church; however, let each one of you love his wife as himself, and let the wife see that she respects her husband.”
This passage is rich with meaning. Clearly the Church is going through a constant process of sanctification. The Church is the body of Christ. The Church is the bride of Christ. Notice all of the language of love and the parallels of husband and wife. Notice that this is all a profound mystery. None of this is a denial of the true Church (i.e. the Catholic Church), but is instead a reference to the sanctification and perfection of the body of Christ. If anything, the passage would support the notion that the Church has imperfections. If this is true then the imperfections cannot therefore invalidate it status. The perfection of the Church is a work in progress. For the Church to be without wrinkle or blemish would require that every member be without spot or blemish, and we know that none of us is perfect. Sanctification is a process for both the individual and the Church.
The indefectibility of the Church is a different issue relative to the content of this post, and I in no way take exception to the comment of Matt16_18.