After Christian pro-democracy activist Joshua Wong was sentenced to six months in prison for his role in the 2014 street demonstrations for freer elections of Hong Kong's leader, his mother reminded him to be courageous like his namesake, Joshua of the Old Testament.

In a letter penned to Wong, 20, just before his his sentence was handed down on Thursday, Grace Ng Chau-mei referenced the biblical figure Joshua, who led the Israelites in the conquest of God's "Promised Land" in Canaan.

She wrote: "Dad and I gave you this name 'Joshua'. So don't forget what God told Joshua: reflect on whatever you do, follow the truth, and you can be courageous."

The New York Times reports that on Thursday, Hong Kong's Court of Appeal sentenced Wong, Nathan Law Kwun-chung and Alex Chow Yong-kang to six to eight months in jail for storming the government headquarters compound at ­Tamar prior to the headline-grabbing "Umbrella Movement" protests three years ago.

At the time, Hong Kong police arrested more than 900 people during the 11-week demonstrations, which forced streets in several major business districts to shut down for almost three months.

"The government wanted to stop us from running in elections, and directly suppress our movement," Wong said in an interview before the decision on Thursday afternoon. "There's no longer rule of law in Hong Kong, it's rule by law."

Originally, the three young men were sentenced to community service and a suspended jail term. However, they were given the prison sentences by an appeals court after the local government pushed for harsher punishments.

In a statement, the Hong Kong Department of Justice claimed that the three protest leaders "were convicted not because they exercised their civil liberties, but because their conduct during the protest contravened the law."

By law, the prison terms left the activists ineligible for public office for five years.

In her letter, Wong's mother said the government's pursuit of the three young men suggested the city had become "depraved".

"The justice department vowed to imprison them based on what they said ... and to eliminate young people's passion and ideals, as well as their vision and commitment for the society," she wrote.

"Why is Hong Kong so depraved now to be treating this generation of children like this?"

Following the sentencing, Wong posted a defiant message on Twitter, vowing to continue his activism.

"They can silence protests, remove us from the legislature and lock us up. But they will not win the hearts and minds of Hongkongers," he tweeted.

As earlier reported, Wong, who spent nights jail after arrests over the demonstrations and endured a lengthy hunger strike, was raised in a Christian family and has in the past told multiple outlets that his faith is the driving forced behind his activism.

Born into a middle-class Christian family and educated at United Christian College (Kowloon East), a private Christian middle school, Wong's passion for positive change started at an early age, as his father began taking him to poorer areas of Hong Kong when he was a young child to impress upon him the need for social reform.

"He told me that I should care for the abandoned in the city. They had not heard of the gospel, and were living solitary and hard lives," he wrote in a blog, according to the SCMP.

"Political reform is the core problem for every issue," said Wong. "Everyone knows that under the Chinese Communist party, there is a lack of possibility to fight [for] true universal suffrage in the end . . . but students should stand on the front line in every century."