Tim Keller says he and his wife Kathy would never want to return the prayer life they had before he was diagnosed with cancer.

The popular pastor and author said on Premier's "Unbelievable?" that he always thought his prayer life was good until he had cancer. 

The 72 year old said that living with cancer over the last two years had made the words in Psalm 90:14 come alive.

The passage reads, "Satisfy us in the morning with your unfailing love, that we may sing for joy and be glad all our days."

Reflecting on his experience, he said, "This is going to sound like an exaggeration. My wife and I would never want to go back to the kind of prayer life and spiritual life we had before the cancer, never." 

He added, "When it comes to prayer, I really thought that I had a good prayer life. And when I broke through to another dimension, I realized my goodness, ... my prayer life wasn't very good." 

Keller said that being diagnosed with stage 4 pancreatic cancer hasn't just changed his prayer life but "everything".

He even went as far as to say that he and Kathy often feel like "we're having a much better life now". 

"[Knowing] you are really going to die changes the way you look at your time, the way you look at God, the way you look at your spouse," he said.

"Everything just changes when you actually realize time is limited and I'm mortal."

He's also appreciating the slower pace of life that has come from living with cancer because, in hindsight, he feels like he was "too active for too long". 

"I'm closer to where I should've been most of my life," he said.

"I'm very blessed in that ... my relationship with my sons are good; my sons are believers. I've got a great relationship with my wife, and that is nothing but God's grace because I was too active," he said. 

Keller admitted, though, that feelings of anxiety with cancer are common, especially when it's time for another scan.

"You know that it doesn't matter how good the last one was. This one could show that it's out of control," he said. 

When the feelings of anxiety come, he turns to the Psalms.

"There's nothing like the Psalms to teach you," he said. "The way I deal with the anxiety is I keep my Psalms up, and I keep my exercise up."