"If we do not register to vote, we will have the authorities we deserve, but if we enlist and vote, we can hold them to account," he told Reuters after Sunday's service.
With presidential elections just months away, he had an earthly message to deliver alongside the psalms and the sermon. He told the worshippers to follow his lead, hold up their cards and show they had registered.
Preparations are underway just as Congo, home to 45 million Catholics - the most of any African country - prepares for the arrival next week of Pope Francis, the first papal visit since 1985.
Democratic Republic of Congo's Catholic church has a long history of promoting democracy in the vast African country where organizing elections has been complicated by financial and logistical problems, and where disputes over vote tampering have frequently caused widespread unrest.
Amid the chaos, the Catholic church deployed thousands of observers across the country before and during voting. Sometimes, as was the case in the 2018 polls, its tallies - trusted by millions - have clashed with official results, raising concerns of fraud.
"The church has a duty to denounce what is wrong with society," Ntambwe said.
Once again, the church is gearing up to monitor elections scheduled for December in which President Felix Tshisekedi will seek a second term in office.
Across the DRC, the Catholic church is already in election mode. Abbots in Kinshasa are encouraging congregants to participate. The church has erected street banners urging people to enroll.
This year, for the first time, the National Episcopal Conference of Congo (CENCO) has partnered up with the Church of Christ of Congo (ECC), a union of 64 Protestant and Evangelical denominations.
Equipped with a book and a cap with the CENCO logo, Nancy Makola took notes. She is one of 600 accredited observers overseeing the registration process, a number that will likely swell into the tens of thousands when voting gets underway in December.
Machine malfunctions were common, Makola added, a detail she later reported to CENCO at their headquarters.
Based on this and more than 1,500 other observer reports, CENCO and the ECC on Thursday recommended that the election commission, CENI, extend the registration deadline.
CENI acknowledged that some registration centres were not functioning properly, without elaborating. It extended the deadline on Sunday by 25 days, until Feb. 17.
For Reverend Nsenga Nshimba, the Secretary General of the ECC, the observations made during the first phase of registrations will prevent problems elsewhere.
"In order not to have a slip, we must learn the lessons of this first area," he said.
