Article VII—Of the Church
Also they teach that one holy Church is to continue forever. But the Church is the congregation of saints [the assembly of all believers], in which the Gospel is rightly taught [purely preached] and the Sacraments rightly administered [according to the Gospel].
And unto the true unity of the Church, it is sufficient to agree concerning the doctrine of the Gospel and the administration of the Sacraments. Nor is it necessary that human traditions, rites, or ceremonies instituted by men should be alike everywhere, as St. Paul saith: ‘There is one faith, one baptism, one God and Father of all.’
Article VIII—What the Church is
Though the Church be properly the congregation of saints and true believers, yet seeing that in this life many hypocrites and evil persons are mingled with it, it is lawful to use the Sacraments administered by evil men, according to the voice of Christ (Matt 23.2): ‘The scribes and the Pharisees sit in Moses’ seat,’ and the words following. And the Sacraments and the Word are effectual, by reason of the institution and commandment of Christ, though they be delivered by evil men.
They condemn the Donatists and such like, who denied that it was lawful to use the ministry of evil men in the Church, and held that the ministry of evil men is useless and without effect.
Although detailed discussion is impossible, a word of explanation will be helpful. These Lutheran confessors, fighting as they were against both the Romanists and the Anabaptists, believed that the word and sacraments formed the church, since through them the Holy Spirit creates faith. They did not believe that the word and sacraments were the boundaries of the church. This led them to suppose that, although they had defined the church as a congregation of saints, the church could still be full of unbelievers.
Baptists later argued that the church is an assembly of saints in the full meaning of that phrase. In other words, we believe in regenerate church membership. We acknowledge that there may be unbelievers who slip into the church, but we deny that any true church can be largely composed of unbelievers. This makes it highly incongruent for "evil men" to be administering the ordinances of baptism and the Lord's Supper. The Second London Baptist Confession says, "These holy ordinances are to be administered by those only, who are qualified and thereunto called according to the commission of Christ" (Chap. 28.2).