zeal

a feeling of strong eagerness (usually in favor of a person or cause)

Passionate ardor in the pursuit of anything; eagerness in favor of a person or cause; ardent and active interest; engagedness; enthusiasm; fervor.

Old French zele, from Latin zelus

“Hadrian." The wise youth returned to Lady Blandish, and informed her of Benson's zeal.”

— George Meredith, Complete Project Gutenberg Works of George Meredith

“They were subsequently united in the 10th century and, with the zeal of new converts, launched several campaigns against the "Sudanese" (pagan peoples of sub-Saharan Africa).”