Neither spelling nor grammar were standardized in the 17th and 18th century. You will find examples of various random capitalization throughout material written at the time. There was no hard and fast rule, though as in the example you gave, often particular words of importance might be highlighted with capitalization.
Capitalisation of nouns in English in the 17th and 18th centuries?
2 Answers By Expert Tutors

Jim M. answered 05/05/19
Published Poet and Author
Good question. As a Germanic language where all nouns were capitalized, English held onto that tradition for quite a while. Perhaps it was German aggression from Prussia and the like that caused British English to become more Latinized. (Latin has few capitalized words. The Greek doesn't at all.) Maybe it had something to do with British colonization, too, which was worldwide. By the time of the American revolution, German troops, known as Hessians, were mercenaries, a full 30% of Britain's fighters, which would not have been probable if Germany was on the ascent at the time. The 17th and 18th centuries, the 1600s and 1700s, were riddled by the Counter-Reformation and the superpower status of Great Britain, plus the growing influence of the Enlightenment or Age of Reason, which spurred on nationalism and anti-Christian liberalism/humanism as byproducts.
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