Zeal

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

A zealot.

To be zealous.

excessive fervor to do something or accomplish some end; "he had an absolute zeal for litigation"

a feeling of strong eagerness (usually in favor of a person or cause); "they were imbued with a revolutionary ardor"; "he felt a kind of religious zeal"

prompt willingness; "readiness to continue discussions"; "they showed no eagerness to spread the gospel"; "they disliked his zeal in demonstrating his superiority"; "he tried to explain his forwardness in battle"