to ask someone in a formal way to do something

They're calling on all men and boys over the age of 14 to join the army. 他们号召所有14岁以上的男子参军。

formal I now call on everyone to raise a glass to the happy couple. 现在我提议大家为这幸福的一对举杯。

to use something, especially a quality that you have, in order to achieve something

She would have to call on all her strength if she was to survive the next few months. 要想渡过未来几个月的难关，她就必须竭尽全力。