The Collaborative International Dictionary
To put one one's mettle
Mettle \Met"tle\, n. [E. metal, used in a tropical sense in allusion to the temper of the metal of a sword blade. See Metal.] Substance or quality of temperament; spirit, esp. as regards honor, courage, fortitude, ardor, etc.; disposition; -- usually in a good sense; as, to test a person's mettle.
A certain critical hour which shall . . . try what
mettle his heart is made of.
--South.
Gentlemen of brave mettle.
--Shak.
The winged courser, like a generous horse,
Shows most true mettle when you check his course.
--Pope.
To put one one's mettle, to cause or incite one to use one's best efforts.