What motivated Dr David Livingstone (1813-73) in his work in Africa?

Born of humble beginnings in a Scottish mill-town, David Livingstone would become one of the great explorers of the 19th century, traversing 30,000 miles of unknown Africa. His pioneering spirit and inquisitive mind brought knowledge and discoveries in the fields of tropical medicine, linguistics, botany, zoology, anthropology and geology. While it can be argued that Livingstone exhibited contradictions and shortcomings as a man, he nonetheless grasped the imagination of Victorian Britain and helped to change European attitudes towards Africa forever. His numerous endeavours were undertaken under the banner of divinely inspired missionary work -- 'If God has accepted my service, then my life is charmed till my work is done' (Livingstone D. Livingstone's Private Journals, 1851-53. London: Chatto & Windus, 1960:108). Yet whether it was indeed religion that truly motivated Livingstone, or rather that he used it as a vehicle for his other passions, is less certain.