Speaking at Bishop Eamon Casey's funeral Mass at Galway Cathedral, the Bishop of Achonry Brendan Kelly also said the wounds caused by his actions were still healing in some of the people who looked up to him.
Most Rev Eamon Casey died aged 89 on Monday. In 1992 it emerged he'd secretly fathered a child with an American divorcee, paying her thousands for their son Peter's upkeep in the US.
However Brendan Kelly also acknowledged Casey's work for his bravery and work for the poor with the aid charity Trocaire, calling him "a defender of the rights of people who were oppressed".
He told mourners about Bishop Casey's courage in helping dozens of injured people in 1980 in El Salvador when soldiers opened fire at the funeral of his murdered friend Archbishop Oscar Romero. 50 mourners died.
"There are those of us who remember, with gratitude, his kindness and encouragement when personally we most needed it," he said.
The bishop added: "Then 25 years ago, the emergence into the light of other hidden realities in his life, beginning with the fact that he had a son, Peter, were profoundly upsetting for the Church and for people in general.
"Yes, we are all sinners, but irresponsibility, infidelity and sin are particularly shocking in the lives of those who preach the Gospel."
