The deranged swordsman attacked the church during a packed Sunday mass on February 11, a Christian persecution watchdog has revealed.
Members of St Lidwina church in Yogyakarta were forced to flee in terror when the man burst into the Catholic church and began slashing at terrified worshippers and clergy members.
Four people were injured in the attack, including Pastor Karl, who was hurt while trying to protect his congregation from the suspected Islamic terrorist.
Two worshipers were also hurt by the man along with a police officer who eventually wrestled the sword away from the attacker.
The attacker has been identified as an Islamic extremist who lived close by the church. He had previously expressed interest in travelling to Syria and “had showed signs of being radicalised”.
Christian persecution watchdog Open Doors said Christians in Indonesia had been subjected to a wave of attacks in recent weeks and called for more assistance.
President Joko Widodo has vowed to uphold religious freedom in the country, which is fighting an increasingly strained battle against extremism.
He said in response to the attack: “Our constitution guarantees religious freedom. Therefore, we will not give even the slightest amount of room to those who promote and spread intolerance in our country. Especially those who act with violence.
“I have ordered the authorities to take firm actions. The state will consequently uphold the constitution.”
Open Doors warned the situation could deteriorate further as local elections approach.
A spokesman for Open Doors said: “Many are concerned for the safety of churches and believers in Indonesia as local elections are scheduled for June.
“Election years are extremely prone to religious conflict which political actors will manipulate to gain votes.”
He warned Islamic extremists were carrying out a campaign of terror on the Asian state, resulting in the violent targeting of Christian converts.
The spokesman: “Radical Islamic leaders are able to mobilise hundreds of thousands of demonstrators on the streets in mass protests against Christians.
“Churches who are seen to be converting Muslims face opposition from extremist Islamic groups. Many converts from Islam experience isolation and verbal abuse because of their faith.”