"He's an academic, a very clear thinker. He would have pondered deeply and prayed about the decision but in the end would have come to it with ease," Bishop Drennan said.
The bishop, who was diocesan chancellor of the Diocese of Christchurch when the deadly February 22 earthquake struck, was in Rome in November and noticed that Pope Benedict had slowed up.
But while his physical health had deteriorated to the point that he walked with a stick, his mind remained as sharp as ever.
It was age taking its toll, rather than the enormous pressures of heading the Catholic Church and dealing with the child sex abuse scandal, Bishop Drennan said.
Benedict's reign would be remembered for his clear, accessible and incisive teaching, a masterful analysis of social trends, but also for his personal humility and kindness.
The Archbishop of Wellington, the Most Rev John Dew, said Benedict would be thought of as a Pope who was faithful and humble in his papacy and in his decision to step down when age and frailty meant he was unable to continue.
"As a great theologian and writer he has at times expressed his desire to spend more time writing and in study; we hope that he has the opportunity to do this in retirement and continue to make a valuable contribution in this way," he said. "The Pope is the shepherd of the Church around the world; this is a demanding and challenging ministry, we pray at this time for Pope Benedict's successor and for the future of the Catholic Church and its leadership."
While it was unusual for a pontiff to step down - the first in 600 years - Archbishop Dew supported Pope Benedict.
"It's taken the Catholic world by surprise," he said.
While it was sad news that Benedict's papacy was coming to an end, Archbishop Dew described the decision as remarkable and courageous.
"He could see there was no point in staying on if he was not able to do what he was elected to do. He just wanted to do the best for the Church.
"We understand the humility, prayer and reflection that will have been behind this decision to step down owing to frailty. We offer the Pope our assurance that we will continue to pray for him. We will also pray for our cardinals who will ... elect a successor.
"His resignation, while unusual, does reflect the pace and workload that this special ministry requires, especially in our modern age."
The cardinals will now gather in Rome to decide on a successor and Archbishop Dew said they would already be thinking about the kind of person best suited for the job.
He believed they would take Benedict's unprecedented decision into account and consider a younger, fitter successor.
Pope John Paul II, elected as a sprightly 58-year old, was able to "stride around the world stage" and bring boundless energy to the role, Archbishop Dew said.
Bishop Patrick Dunn of Auckland was moved by the boldness of the decision, saying it set an interesting precedent for any successor.
