volunteer to do sth/recommend oneself
In the Warring States Period, the State of Qin besieged the capital of the State of Zhao.
A man called Mao Sui volunteered.
When the negotiactions between the two states were stalled because the ruler of Chu hesitated to send troops, Mao Sui approached him, brandishing a sword. At that, the ruler of Chu agreed to help Zhao, against Qin.
This idiom means to recommend oneself.