The comments sparked widespread anger in the world's most populous Muslim-majority country and the case is now seen in part as a test of religious tolerance in Indonesia.
But critics say it is also about politics as the governor's foes whip up anger to reduce his support. Purnama, better known by his nickname Ahok, is Jakarta's first non-Muslim governor for half a century and a member of the country's tiny ethnic Chinese minority.
The 50-year-old has won huge popularity with his no-nonsense style and determination to clean up Jakarta, an overcrowded, disorganised and polluted metropolis of 10 million.
But he has also faced constant opposition from hardline Islamic groups, who dislike a non-Muslim being in charge of Indonesia's capital. He is running for election in February.
During a campaign stop in September, Purnama told a crowd they had been "deceived" by his opponents who used a verse from religious text to try to put them off voting for a Christian.
The speech went viral, angering moderate and conservative Muslims alike who considered the remarks offensive. Purnama apologised but Indonesia's top Islamic clerical body declared the remarks blasphemous.
In November more than 100,000 Muslims swarmed Jakarta in one of the largest mass demonstrations seen in the capital in years as hardliners burnt cars and clashed with police, demanding Purnama face justice.
President Joko Widodo vowed to swiftly resolve the case, and police officially declared Purnama a suspect for blasphemy. Indonesia's constitution guarantees freedom of religion but officially only six faiths are recognised.
Under tough laws dating back to 1965, anyone who insults these religions or deviates from their beliefs can be charged with blasphemy and jailed. Critics say today the laws are exploited to persecute minorities, like Shia and Ahmadi Muslims, and in some cases, even atheists have fallen foul of the legislation.
In 2012, a man was sentenced to two-and-a-half years prison for writing "God does not exist" on Facebook. The race to run Jakarta - Indonesia's financial and political capital - has been a launch pad for the presidency and is always closely watched.
But this election, fuelled by the blasphemy controversy, is shaping up as a key battleground for Indonesia's most powerful political factions. Purnama is running against two Muslim opponents: the son of former president Susilo Bambang Yudhoyono, and a popular ex-education minister backed by 2014 presidential runner-up Prabowo Subianto.