Doctor Nagel's chief insight, in my opinion, is that we should receive the gifts of God as he gives them. When we start cutting them into pieces - always with the excuse of figuring out a hard case, or of gaining greater theological acuity - we mess it up. This brilliantly simple and clear insight works with so many topics: family morality (sex, marriage, babies: one gift), the apostolic succession (Office of the Ministry is one gift - you can't cut the presbyter bit out of the apostle and only give that to some guys while giving the whole episkopos shebang to another), and here with the Ministry and the Bible.
Luke actually takes the time to really drive this home to us in the Acts of the Apostles. In chapter 8, with Philip and Ethiopian, we see that while the Church only knows doctrine from the Scriptures (sola Scriptura), she never knows a Scripture that is alone apart from the Ministry. "How can I understand what I read unless someone guide me?" Indeed! Ministry and Word - a gift given together. But just so that you don't get the wrong idea , a few chapters later we have the Bereans. Even an apostle is not to be believed just because he says so - the Bereans are noble for keeping the ministry connected to the Word by holding the minister to the Word.
So can a person become a Christian apart from the ministry? Can a person become a Christian apart from the Scriptures? Refer the person asking the first to the Ethiopian and the person asking the second to the Bereans.