|The views of Voltaire on religion, ranked by James Haught (1996) as one of the top 64 disbelievers (#9) of history, is an intricate one: in 1759, in his Candice, he made a parody out of Gottfried Leibniz’s proposed solution to the problem of evil; sometime thereabouts he discovered the 1829 closet extreme atheism work of Jean Meslier, and into the 1760s began to promote Meslier’s anti-Catholic views and proofs. In 1769, Voltaire published God and Human Beings, wherein he presents one of the first comprehensive works on comparative religion and mythology.|
Pascal | Descartes
In 1733, Voltaire, in his Philosophical Letters, satirized the religious teachings of Rene Descartes and Blaise Pascal, including Pascal's famed "wager" on God. Voltaire wrote: "The interest I have in believing a thing is not a proof of the existence of that thing." Voltaire's French publisher was sent to the Bastille and Voltaire had to escape from Paris again, as judges sentenced the book to be "torn and burned in the Palace." (Ѻ)
In 1759, Voltaire penned his satirical Candice, a parody of Gottfried Leibniz’s problem of evil solution, the key section being the following: “Appalled, stupefied, distraught, covered in blood and shaking uncontrollably, Candice said to himself: ‘If this is the best of all possible worlds, what must the others be like?’”
German philosopher Arthur Schopenhauer, the first "admitted and inexorable atheist" (Friedrich Nietzsche, 1882) among Germans, commented the following: 
“I cannot assign to the Theodicy any other merit than that it gave rise to the immortal Candice of the great Voltaire. In this way, of course, Leibniz’s oft-repeated and lame excuse for the evil of the world, namely that the bad sometimes produces the good, obtained proof that for him was unexpected.”
In circa 1759, Voltaire obtained a copy of French closet atheist priest Jean Meslier's Testament (1729), wherein he explicitly denies the existence of god, denies the existence of the soul, dismissed the notion of free will, denounces all belief in an associated with god, and all religions, Christianity in particular, with a “frenzied anger that makes Richard Dawkins’ The God Delusion seem like a work of reasoned scholarship”, as atheism historian Nick Spencer (2014) puts it. Voltaire, however, found the Meslier’s atheism too extreme for his tastes; or at least too extreme to be sided with publicly. The gist of the situation, in this time in history, is summarized well by Michel Onfray as follows: 
“Meslier’s war cry [Testament, 1729], never before heard in the history of western thought, offers one of the first true atheist moments, if not the first. Prior to him, they call the agnostic an atheist who, as Protagoras, concludes that when it comes to god one can conclude nothing; the pantheist who, such as Spinoza, affirms its existence consubstantial with nature; the polytheist, like Epicurus, who teaches its multiplicity; the deist, in the way of Voltaire, for whom god creates the world en bloc, but does not care about the details; or whoever’s idol does not correspond to the strict criteria established by the church. Now, the atheist clearly says that ‘god does not exist’. This is what Meslier clearly writes: ‘there is no god’ (chapters 59, 74, 93, 94)—that is clear and distinct, blunt, and straightforward.”
In 1761, Voltaire published corrupted version of Meslier’s work entitled Extract of the Sentiments of Jean Meslier, wherein he omits the author’s materialism and atheism, and focuses on his anti-Catholicism to serve his own purpose, and asserts falsely that Meslier asked for forgiveness on his death bed for writing such blasphemy; resultantly, Meslier, as Michael Onfray (2009) put it, becomes the “shield of Voltaire” and his anti-Catholic deism crusade. The following are a number of communicates, in the 1760s, of Voltaire promoting Meslier:
“Apropos, they have lent me that work attributed to St. Evremon, and which is said to be by Dumarsais, of which you spoke to me some time ago; it is good, but the Testament of Meslier is still better!”— Jean d’Alembert (1764), “Letter to Voltaire”, Jul 9
“They have sent me two abstracts of Jean Meslier. It is true that it written in the style of a carriage-horse, but it is well suited to the street. And what testimony! That of a priest who asks pardon in dying, for having taught absurd and horrible things! What an answer to the platitudes of fanatics who have the audacity to assert that philosophy is but the fruit of libertinage!”— Helvetius (1763), “Letter to Voltaire”, May 1
“The Testament of Meslier ought to be in the pocket of all honest men; a good priest, full of candor, who asks god’s pardon for deceiving himself, must enlighten those who deceive themselves.”— Voltaire (1764), “Letter to Ferney”, Jul 16.
“Meslier’s Testament is the most singular phenomenon ever seen among all the meteors fatal to the Christian religion.”— Voltaire (1766) 
In 1772, Baron d’Holbach published, albeit anonymously, an atheism explicit version of Meslier’s work entitled Common Sense, which included some of the above commentary.
In 1769, Voltaire, penned his God and Human Beings, one of the first works in comparative religion and mythology. 
Lord Byron, early on, read enough of Voltaire and David Hume to become a skeptical agnostic leaning towards atheism. 
Quotes | Related
The following are other related Voltaire content quotes:
“It is very important not to mistake hemlock for parsley; but not at all so to believe or not in god.”— Denis Diderot (c.1765), “Response to Voltaire” 
The following are other related quotes by Voltaire:
“The Bible. That is what fools have written, what imbeciles command, what rogues teach, and the young children are made to learn by heart.”— Voltaire (c.1750) 
“I want my lawyer, my tailor, my servants, even my wife to believe in god, because it means that I shall be cheated and robbed and cuckolded less often. ... If god did not exist, it would be necessary to invent him.”— Voltaire (c.1760) 
“Atheism is the vice of a few intelligent people.”— Voltaire (1764), Philosophical Dictionary (Ѻ)
“There are not sects in geometry.”— Voltaire (1764), Philosophical Dictionary (Ѻ)
1. God – OnlineEtymologyDictionary.com.
2. (a) Palmer, Michael. (2013). Atheism for Beginners: a Coursebook for Schools and Colleges (pg. 194). Lutterworth Press.
(b) Meslier, Jean. (1729). Superstition in All Ages (editor: Baron d’Holbach; translator: Anna Knoop) (Ѻ). Publisher, 1878.
3. (a) Herrick, Jim (1985). Against the Faith (pg. 75). Glover & Blair.
(b) Borne, Étienne (1961). Atheism (pg. #). Hawthorn Books.
4. Voltaire. (2010). God and Human Beings (translator: Michael Shreve; Introduction: S.T. Joshi). Prometheus Books.
5. Flynn, Tom. (2007). The New Encyclopedia of Unbelief (foreword: Richard Dawkins) (Voltaire, 60+ pgs.). Prometheus Books.
6. (a) Jorgensen, Larry M. and Newlands, Samuel. (2014). “Introduction”, in: New Essays on Leibniz’s Theodicy (pg. 4). Oxford University Press.
(b) Nietzsche, Friedrich. (1882). The Gay Science (Ѻ). Publisher.
7. Onfray, Michael. (2009). “The War Song of an Atheist Priest”, in: Testament: Memoir of the Thoughts and Sentiments of Jean Meslier (translator: Michael Shreve) (Preface, pgs. 17-24; quote, pg. 19). Prometheus Books.
8. Konner, Joan. (2007). The Atheist’s Bible: an Illustrious Collection of Irreverent Thoughts (Voltaire, pg. 66). Harper Collins.
● Morehouse, Andrew. (1932). Voltaire and Jean Meslier: The Influence of Jean Meslier on Voltaire. Harvard University.
● Stephens, Mitchell. (2014). Imagine There’s No Heaven: How Atheism Helped Create the Modern World (Voltaire, 54+ pgs). Plagrave Macmillan.
● Voltaire quotes – PositiveAtheism.com.