Voltaire is advocating philosophical skepticism.
Pangloss embodies the optimistic notion that ultimate reality can be known by reason, and Martin embodies the pessimistic notion that ultimate reality defies a rational accounting and can be known only through a manichaeistic mythology.
Cacambo embodies the notion that one cannot know whether or not ultimate reality can be proved by reason.
From the text:
"I do not know," answered the worthy man, "and I have not known the name of any Mufti, nor of any Vizier. I am entirely ignorant of the event you mention; I presume in general that they who meddle with the administration of public affairs die sometimes miserably, and that they deserve it; but I never trouble my head about what is transacting at Constantinople; I content myself with sending there for sale the fruits of the garden which I cultivate." ... "I have only twenty acres," replied the old man; "I and my children cultivate them; our labour preserves us from three great evils—weariness, vice, and want."
"Let us work," said Martin, "without disputing; it is the only way to render life tolerable."
"All that is very well," answered Candide, "but let us cultivate our garden."
His famous conclusion in Candide, for example, that optimism was a philosophical chimera produced when dialectical reason remains detached from brute empirical facts owed a great debt to his Newtonian convictions.
His alternative offered in the same text of a life devoted to simple tasks with clear, tangible, and most importantly useful ends was also derived from the utilitarian discourse that Newtonians also used to justify their science.