Verified answer

These are my thoughts on it.

Brutus was troubled by his decision to take part in the plot to murder Caesar, his friend and the great hero of Rome.

His wife wanted to know what was bothering him but at first he wouldn't tell her. She was inclined to be in poor health and this may be one of the reasons he didn't tell her about his plans. Because he was afraid that worrying about him would make her ill.

She eventually wounded herself in the thigh to prove that even though she was a "weak" woman and often ill, she still had the strength to be Brutus' confidante (as a wife ought to be).

This could be view as a "noble" act on her part, to endure pain to prove her worth. Brutus could be making a general prayer out loud that he would be found worthy of being married to such a noble, strong woman.

Also bear in mind that she was the daughter of a noble roman named Cato and the wife of Brutus himself a noble roman. So the line probably has more than one meaning.