The Rev. Kenneth Kuntz said the events of last week are "beyond our ability to comprehend.
"No words can describe the depth of emotion we feel in our hearts," Kuntz said.
Six caskets rested end-to-end at the front of the church. Flowers and a photo of each family member sat next to each casket. Behind the caskets stood two enlarged family photos, including one of the family in front of a Christmas tree.
Many mourners dabbed tears from their eyes as they entered the sanctuary, which was awash in reds, greens, yellows and blues from the sun shining through the stained-glass windows.
Kuntz described how the entire Sueppel family attended Easter Mass hours before police believe the slayings began.
He briefly focused on the problems facing Steven Sueppel, who had been indicted last fall on federal charges accusing him of embezzling nearly $560,000 from Hills Bank & Trust, where he once worked.
"The scourge of mental illness leaves us bewildered, confused and even angry," Kuntz said.
Also killed were Sheryl Sueppel, 42, Ethan, 10, Seth, 8, Mira, 5, and Eleanor, 3.