"Utter seriousness" means complete and total seriousness. It refers to situations or actions taken very seriously without any hint of humor or lightness. Full definition
We must, with utter seriousness, address the question of whether it is possible to be an agent of transformation in such a setting. (religion-online.org)
Why do so many southern Christians take with utter seriousness spiritual things that seem to most of us as outmoded leftovers from a redundant worldview? (firstthings.com)