The Last Christian by David Gregory

A.D. 2088. Missionary daughter Abigail Caldwell emerges from the jungle for the first time in her thirty-four years, the sole survivor of a mysterious disease that killed everyone else in her village. After receiving a curious message from her grandfather, Abby goes to America, only to discover a nation that has that has become completely secularized and all religion has died away. A curious message from her grandfather assigns her a surprising mission: re-introduce God to America, no matter how insurmountable the odds.
But a larger threat looms. The world's leading artificial intelligence industrialist has perfected a technique for downloading the human brain into a silicon form. Brain transplants have begun, and with them comes the promise of eternal existence. Abby and Professor Creighton Daniels, a historian troubled by the mystery of his father's sudden death, uncover a plot to force the entire planet to convert to this 'transhuman' status--and forever lose all possibility of a connection with God. Together, they begin to unravel the conspiracy, attracting the attention of the powerful and devious men behind it. In a race for their lives, Abby and Creighton search for the truth while humanity's spiritual future hangs in the balance.