There is but one God essentially considered: and in this the Scripture is clear, and so in this Book [Revelation], chap. 1. and last; although there be a plurality of Persons mentioned, yet it is ever God spoken of as One, in the singular number; and thus He is still opposed as the One living God, to the plurality of Idols.
And indeed, there can be no plurality in this: for, if that One God have in Him all perfections, There can be no perfection beside Him; and so no God beside this One true God. And, if we supposed any perfection to be beside Him, then were not He God, because not infinite in perfection; and, if infinite, then that which is infinite, in that respect, cannot be multiplied. There is no question of this, seeing the most wise Heathens have been necessitated to acknowledge it.
James Durham, A commentary upon the book of the Revelation. Wherein the text is explained, the series of the several prophecies contained in that book, deduced according to their order and dependence on each other; the periods and succession of times, at, or about which, these prophecies, that are already fulfilled, began to be, and were more fully accomplished, fixed and applied according to history; and those that are yet to be fulfilled, modestly, and so far as is warrantable, enquired into. Together with some practical observations, and several digressions, necessary for vindicating, clearing, and confirming many weighty and important truths (Edinburgh: Christopher Higgins, 1658), p. 6.