From this article by EV. I've put Locke's words in bold so as not to confuse when Locke is speaking and when EV is commenting on Locke's words:
The last step [of something] is taken by Locke in the Essay Concerning Human Understanding. "Reason is natural revelation, whereby the Father of Light and fountain of all knowledge, communicates to mankind that portion of truth which he has laid within the reach of their natural faculties."
This part of the passage sounds comparatively harmless, so harmless that in isolation it could perhaps be taken as Thomistic in meaning.
The sequel is less harmless:Revelation is natural reason enlarged by a new set of discoveries communicated by God immediately, which Reason vouches the truth of, by the testimony and proofs it gives that they come from God. So that he that takes away Reason to make a way for Revelation, puts out the light of both, and does much the same as if he would persuade a man to put out his eyes, the better to receive the remote light of an invisible star by a telescope.
Now, indeed, Reason is made the judge of the truth of Revelation. "Whatsoever God hath revealed is certainly true. No doubt can be made of it. But whether it be a Divine Revelation or no, Reason must judge, which can never permit the mind to reject a greater evidence for that which is less evident, or prefer less certainty to greater."
The bond of faith is broken and the experiences that give meaning to the symbols of myth and religion are lost.
At American Creation we've longed discussed Locke being the philosophical mentor of America's Founders, especially on their political-theological issues. Was it traditional Christianity? Was it Thomism? Was it Enlightenment rationalism? Where does one end and the other begin? EV seems to cite Locke for the proposition of reason trumping revelation or reason determining what is legitimate revelation from God. This differs from Leo Strauss' Locke as a secret atheist, but is consonant with Gregg Frazer's notion of theistic rationalism that posits a partially inspired Bible, one that is errant and fallible and of which man's reason determines the valid parts.