"It's impossible to make sense of such violence and suffering. Those whose lives were taken did nothing to deserve their fate. They were simply in the wrong place at the wrong time," Mr Bush said.
"Now they're gone and they leave behind grieving families, grieving housemates and a grieving nation."
He called on the bereaved to draw courage from three "sources of strength" – faith, loved ones and the "passionate and resilient" college spirit of the university.
"As a Dad I can assure you that a parent's love is never far from your child's heart," he added.
The community spirit at VT was emphasised in an address made by Virginia's governor, Tim Kaine, who flew home from trade talks in India to attend the service.
He described the "bitter and sad day" but said that being present in the middle of such an "extraordinary community" had made him feel "very privileged".
"Even in the midst of the darkest day in the history of this campus, what you showed to the world yesterday was an amazing thing. What students came back to was… the incredible community spirit and sense of unity on this campus," he said.
VT's president, Charles Steger, thanked Mr Bush and Mr Kaine for their support and expressed the university's gratitude for the messages of support received from around the world. He said they had "touched us and reaffirmed our basic belief in the goodness of people".
Despite this his remarks concentrated on the depth of feeling felt by the university. Mr Steger explained that all in the VT family wanted to wake from the "horrible nightmare" of what had been the single worst day of violence in American college history.
"There really are no words that truly express the depth of sadness that we feel. In fact, words are very weak symbols of our true emotions at times such as this. It's overwhelming, almost paralysing," he said.
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