Sola Scriptura and Richard Hooker

One of the classic doctrines of the Reformation was Sola Scriptura, but all too often it is misunderstood and misexplained. It's especially helpful to look at what it does and doesn't mean with reference to Richard Hooker and the so-called Regulative Principle.

One of the main Reformation criticisms of the pre-Reformation Catholic Church was that sometimes people in power claimed that it was essential to believe what they said in order to be saved. The Reformer's response to this was to say Sola Scriptura - Scripture alone contains what it is necessary to know for salvation.

That is what the main Reformers believed, and we see it, for example, in the Ordination of Deacons service in the Church of England:

[Question]: Do you accept the Holy Scriptures as revealing all things necessary for eternal salvation through faith in Jesus Christ?
[Answer]: I do so accept them.

But that's not the way a lot of people understand the doctrine of sola scriptura, especially the people who disagree with it. The other approach to it is represented by some of the so-called Radical Reformers such as Grebel, Hooper and Cartwright. Hooper came up with the “Regulative Principle”, which roughly put said that only what is explicitly commanded in Scripture is right to do in church. Cartwright took it further and said

Scripture is the onely rule of all things which in this life may be done by men.

Richard Hooker argued both against the Roman Catholic view that there were things that it was essential to know for salvation that weren't in the Bible and the Radical view that everything that was right was in the Bible. One example he gave was that if we rely on the Bible to tell us absolutely everything rather than just what we need to know to be saved, then we're stuck, because the Bible itself doesn't tell us which books are in the Bible.

The schooles of Rome teach scripture to be so unsufficient, as if, except traditions were added, it did not conteine all revealed and supernaturall truth, which absolutely is necessarie for the children of men in this life to know that they may in the next be saved. Others justly condemning this opinion grow likewise unto a dangerous extremity, as if Scripture did not contain all things in that kind necessary, but all things simply, and in such sort that to do any thing according to any other law were not only unnecessary but even opposite unto salvation, unlawful and sinful.
Richard Hooker, Laws of Ecclesiastical Polity 2.8.7

I tend to agree with Hooker on this. Because of their views that Scripture tells us everything, not just everything we need to know to be saved, the Radicals ended up intepreting large chunks of it out of context and failing to recognise that Jesus is the main character. As Hooker said, “their common ordinarie practice is, to quote by-speeches in some historical narration or other, and to urge them as if they were written in moste exact forme of lawe.”

So what implication does this have for churches that use the Regulative Principle today? I really don't get it. Where does Scripture command the Regulative Principle? Where does Scripture define which books are Scripture and which aren't? Where does Scripture command the hermeneutics you are required to use to understand it in the way you need to if you follow the Regulative Principle?

Interestingly, Hooker was also a fan of the perfection of Scripture, but was very clear that it was perfect for the purpose of telling us everything we need to know to be saved and to be "thoroughly equipped for every good work" rather than perfect for everything.