Definition of "unessential"

[I] have a question more to ask you on occasion of what you have told me; and that is, Whether you are to leave every Minister and Church, as soon as any thing is said that is really erroneous, in the lesser and unessential matters?

1676, Joseph Glanvill, Seasonable Reflections and Discourses, London: R.W. [and] H. Mortlock, p. 92

[He was] moved rather with Pity than Indignation towards the Persons of those, who differed from him in the unessential Parts of Christianity.

1716, Joseph Addison, The Free-Holder, No. 39, 4 May, 1716, London: D. Midwinter and J. Tonson, p. 225

“ […] strangeness is not in the nature of a thing, but in its relation to something extrinsic—in this case an unessential observer.”

1886 May – 1887 April, Thomas Hardy, chapter 18, in The Woodlanders […], volumes (please specify |volume=I to III), London, New York, N.Y.: Macmillan and Co., published 1887

But all this part of it seemed remote and unessential.

1925, F[rancis] Scott Fitzgerald, chapter 9, in The Great Gatsby, New York, N.Y.: Charles Scribner’s Sons, published 1953

These [gates] past, if any pass, the void profoundOf unessential Night receives him nextWide gaping, and with utter loss of beingThreatens him,

1667, John Milton, “Book II”, in Paradise Lost. […], London: […] [Samuel Simmons], […]; republished as Paradise Lost in Ten Books: […], London: Basil Montagu Pickering […], 1873, lines 438-441

[…] even before the Heavens, before those material Orbs, that now rowl over us, were call’d from the dark, and profound Abyss of unessential Nothing:

1686, William Hall, A sermon preach'd before Her Majesty the Queen Dowager‎, London: William Grantham, page 7