He said this at the ordination of 26 priests and 50 years of Sacred Heart Seminary, Nsude (Junior Seminary), in Enugu.
In his homily, the Bishop charged the priests to organise retreats for their parishioners, pay greater attention to prayers, and not hold crusades.
Onaga, who was celebrating his alma mater, warned priests against forming prayer groups but to take their members to approved prayer places like Ugwu Dì Nso, a monastery and others.
“Do not adopt the pentecostal approach of service, and be careful in forming prayer groups,” he charged.
He admonished the newly-ordained priests to seek spiritual holiness and avoid being dragged into secular affairs.
Earlier, the Rector of the seminary, Rev. Fr. Stanislaus Onodugo, said the seminary was the brain-child of Bishop of Enugu, His Lordship Godfrey Okoye, of blessed memory, in 1972.
Onodugo stated that since 1972, priests and lay persons that went through the seminary had graduated into reputable personalities.
He said: “Today, the seminary can boast of at least one bishop who was among the second set to study in this seminary, and that is Bishop Onaga.
“We are also celebrating the grand finale of our golden jubilee, which started since June 27.
“Today, our dear Bishop raised 26 Deacons to the Order of Priesthood and we are happy that such event is happening in our time.”
The News Agency of Nigeria reports that Bishop Onaga was among the second set of students to be admitted into the seminary in 1973.