Six gardaí carried the coffin of colleague Colm Horkan into the church for his funeral today as the song You Raise Me Up was played.
A picture of the murdered garda was displayed on a screen close to the altar.
With limits on the number allowed inside, people gathered outside the church for the service.
Ahead of the funeral, a minute's silence was observed and matched with similar tributes at Garda stations around the country at the same time, including here in Cork.
Minister for Justice Charlie Flanagan and Garda Commissioner Drew Harris joined mourners in the church.
Monsignor Tommy Johnston said Colm Horkan was "deeply loved".
He extended his condolences to his father Marty, his sister Deirdre and his brothers Aiden, Brendan, Dermot and Padraig.
Among symbols left at the altar to represent Colm Horkan's life were his garda notebook, a GAA jersey from his home team in Charlestown and a Liverpool FC tie pin.
His brother Dermot explained the significance of each.
With his voice breaking with emotion, he said: "The Liverpool motto 'you'll never walk alone' summed up Colm perfectly - he never let any of his family or friends walk alone."
In his homily, Monsignor Johnston described the garda as one of nature's gentlemen.
"The gunshots that rang out in the early hours of Wednesday morning echoed not just in the town of Castlerea but right across the country, spreading a story of tragedy and sadness and the loss of life of a detective garda," he said.
"Colm Horkan was a good man, one of nature's gentlemen. That and more, as someone said."
He added: "On Friday night, as his body was brought back home, hundreds of people lined the streets from the GAA pitch to his home. As the hearse passed on its way those lining the street joined in a silent walk of welcome for a man who was dearly loved and respected in the community.
"Old and young gathered for that walk with the various teams, senior and underage, women and men flanking the hearse and the following cars, a silent salute for a man whose voice was gentle and his approach respectful.
"That gentleness and respect earned the goodwill of so many and endeared him to young and old."
The priest said Mr Horkan had a great impact in the communities of Ballaghaderreen and Castlerea where he served.
"Service is such an apt word for Colm for he truly was a man of service, dedicated and diligent," he said.
"Colm loved his life as a guard and gave it his complete commitment.
"One of the good things that have emerged from Covid-19 is that it has helped us to recognise the importance of our frontline workers and up there, very much to the fore, are our guards helping to keep the nation safe.
"Their work never ceases, 24/7 a guard is on duty. In the words of a prayer they 'watch over us while we sleep and protect us while we are awake', under the protection of their patron, Blessed Michael, the Archangel.
"We thank our guards for their commitment and dedication. Long may we be blessed by men and women of true dedication and service, men like Colm Horkan."
Monsignor Johnston acknowledged the death of Colm Horkan had left many people with unanswered questions.
"In the case of Colm, questions have us wonder why did this tragedy happen? Why did Colm die, why was this life, which had so much to offer, taken away so soon?" he said.
"I cannot answer those questions, but it seems when God takes the young he takes only the very best.
"Why? Has God some special task for them? Has God some special task for Colm?
"God's plan has a purpose way beyond our imaginings. Into the darkness of grief, of sadness, of loss, of hurt, of anger God can bring a light of goodness, a ray of hope to open hearts, even fleetingly to the reality of his goodness.
"We pray for a ray of hope, a light of goodness to bring its blessings to those remembering in grief and sadness this good man, Colm."
The priest ended his homily by reading a tribute penned by one of Mr Horkan's friends.
He read: "Colm was a cherished member of our community, a brother to everyone, young and old. We grew up together, played together and performed in school plays together.
"Now we are in shock and deep mourning. We are heartbroken for Colm's family, colleagues and many, many friends.
"It will take a long, long time for our community to come to terms with this senseless act of violence against our brother, Colm.
"Now Colm is God's right-hand man, his very best wingman.
"Now we ask God, surrounded by all the saints and angels in heaven, to wrap Colm in his arms, to comfort and console Colm's family, colleagues and many, many friends, near and far."