As someone noted, "Protestantism" covers quite a chaos of different theories. There was a fault line running through the Calvinist tradition in the 16th & 17th centuries. Affirmation of Scripture as divinely inspired and as the only source of truth was necessary for the battle with Rome. But as even Calvin admitted, an inspired text can only be interpreted by an inspired reader. And at that point, things become potentially (and in a short time, really) hairy, to say the least. For if one must be divinely inspired to construe Scripture accurately, then why need Scripture at all. Milton puts this (in minimal form) into Paradise Regained. Satan offers The Son the wisdom of Athens, and The Son's reply includes the following:
Who therefore seeks in these True wisdom, finds her not, or by delusion Far worse, her false resemblance only meets, An empty cloud. However many books Wise men have said are wearisom; who reads Incessantly, and to his reading brings not A spirit and judgment equal or superior, (And what he brings, what needs he elsewhere seek) Uncertain and unsettl'd still remains, Deep verst in books and shallow in himself, Crude or intoxicate, collecting toys, And trifles for choice matters, worth a spunge; As Children gathering pibles on the shore.
(P.R. IV 319-331)
The Son goes on to affirm that all wisdom is to be found in Scripture; that is, Milton does not _explicitly_ here acknowledge that what is true of the reader of classic works is _also_ true of the reader of Scripture. But the point is clearly there. (Milton, after all, had construed Christ's forbidding of divorce as, actually, approving divorce!) There is, then, a direct line inside Calvinist theology from the "all-sufficiency" of Scripture to antinomianism, the doctrine that God directly inspires individuals in the truth, and hence neither Church nor Scripture is necessary. (I'm reducing thousands of pages of controversy to a few rather crude propositions, but this was the thrust of much of it.)
Calvin recognized this, and one might say he hated it, but in his theoretical works did not draw back from it.
It also drove Dryden nuts. In his fine poem, _Religio Laici_, he tried to defend the "middle way" of the Anglican Church against the RC claim that (again, this is quite reductive) only an inspired Church could be trusted to construe Scripture. But his own argument didn't convince him long, and he converted to the RC.
Carrol