Ardern spoke this morning at Lautoka Mosque as part of her trip to Fiji to remember Imam Hafiz Musa Patel, Ashraf Ali Razak and Ashraf Ali.
She also thanked the Fijian community for their response in the aftermath.
"I want to place on record our deep appreciation for the many messages of support and sympathy we received from Fiji following the March 15 attacks, it gave us strength to know that you stood in solidarity with us.
"But it was especially moving to receive those messages when you faced your own grief," she said.
She said she still recalls visiting the hall the day after the attack where hundreds of members of the Muslim community were gathered.
"Amongst them was the wife of one of your fallen, I still remember talking with her as she desperately looked for her husband and feeling pained to leave her with the Red Cross.
"In your darkest of hours I can tell you I will never forget your grief," she said.
She said she has been so moved by the generosity of the muslim faith.
The grandson of Ashraf Ali Razak, Mohammed Iftikar Ali said it was fate because his grandfather wasn't supposed to be in Christchurch that day, but he made a stop over on his way to Australia to visit a sick relative.
He appreciated the prime minister's visit and said it was comforting.
"She was so warm in how she was explaining how sorry she was, it is none of our fault, but it was fate to be done and we are really thankful for her to be here," he said.
"We really miss who we lost, he can't be replaced."
The niece, Saliman Bibi said Ardern told them she was sorry for their loss.
"I was just lost with words I couldn't say anything, I just felt great she is here, she is with us in our soul," she said.
Ardern also spoke of the commitment to ensure these attacks never happen again.
She then spoke about the moves the government had taken to address weaknesses in gun legislation and to tackle extremist content online.
However, she added it is not just politicians or those in positions of power who can honour those who have died.
"Immediately after the attacks, Prime Minister Bainimarama called on all Fijians across all backgrounds and faiths to join him in making a pledge: where ever you encounter someone who says something racist and hateful, whether it is online or in person, say something.
He said, "Be the voice of love. Be the voice of change."
Today marked the last day of the prime minister's trip to Fiji, this evening she will be leaving for Australia where she will be meeting with Australian Prime Minister Scott Morrison on Friday.