One could interpret much of work of Beethoven by saying that suffering is inevitable, but the courage to fight it renders life worth living.

1. by saying...是介词短语，作“方式状语”。

2. saying 是非谓语，是动名词，作介词by 的宾语。

3. saying 之后接的是宾语从句，宾语从句也是一个句子，当然是自己的谓语。

4. saying 的宾语从句是个并列句，含有两个并列分句，每个分句各有自己的谓语动词：is 和 renders。

【直观分析】

One could interpret （谓语动词）much of work of Beethoven by saying （非谓语动词）that suffering is （宾语从句第一并列分句的谓语动词）inevitable, but the courage to fight it renders （宾语从句第二并列从句的谓语动词）life worth living.