This presupposes an original and necessary law of nature or reason, as insisted on by Hooker.
A pantheist may believe in Law of Nature and go no further; a theist who accepts Law of Nature has a large instalment of natural theology ready made to his hand; including an idealist, or else an intuitionalist, scheme of ethics.
But the moral law must not be conceived under the form of an "imperative" or a "Sollen"; it differs from a law of nature only as being descriptive of the fact that it ranks the mind as conscious will, or zweckdenkend, above nature.
The philosopher in Abelard's Dialogus inter Judaeum Philosophum et Christianum expects to be saved ex sola lege naturali; here " law of nature " is fully equivalent to Natural Religion, and the word sola sets it in contrast with Christianity.
Locke had spent some years in Holland, the country of Grotius, who, with help from other great lawyers, and under a misapprehension as to the meaning of the Roman jus gentium, shaped modern concepts of international law by an appeal to law of nature.