What motivated him, we were to understand, was his zeal for “fundamental fairness”— protecting the taxpayer, controlling spending and ensuring that only the most deserving claimants received their benefits.

参考译文：我们要明白促使他这样做的是要实现“基本公平”的热情——包括保护纳税人的利益，控制开支/支出，且确保只有最值得救济的申请人才能获得他们的救济金。

【1】这个非限制性从句we were to understand，是对 what motivated him 这个名词性从句的修饰嘛？还是对融合性关系代词 what 的修饰，如果修饰 what，可以改成what we were to understand motivated him吗？

解答：we were to understand为插入语，两边都有逗号进行隔开,were to按照情态动词进行理解，后面接动词原形understand. What motivated him

what为连接代词/融合性关系代词/融合性连接代词引导的主语从句(what=the thing that),what引导的主语从句用来作主语的主语，was为系动词,his zeal为主句的表语，for fundamental fairness为介词短语作后置定语修饰前面的名词his zeal. 破折号起解释说明的作用。

【protecting the taxpayer动名词短语(1)】, 【controlling spending动名词短语(2) 】and【ensuring that only the most deserving claimants received their benefits动名词短语(3)】为三个并列动名词短语对前面的名词“fundamental fairness”起进一步解释补充说明，可以理解为.fundamental fairness的同位语。

第3个动名词短语还带有that宾语从句，其语法结构分析如下

ensuring【动名词】// that【从属连词】// only the most deserving claimants 【主语】//received【谓语动词】// their benefits【宾语】

【2】波折号后面的部分是 fundamental fairness 的同位语嘛？

解答：波折号后面的三个并列动名词短语是fundamental fairness的同位语。

以上句子整体语法结构分析如下

What motivated him【主语】,// we were to understand,【插入语 】// was 【系动词】//his zeal【表语】// for “fundamental fairness”【后置定语】—protecting the taxpayer, controlling spending and ensuring that only the most deserving claimants received their benefits【为“fundamental fairness”的同位语】

以上句子去掉所有修饰成分留下主干为：What motivated him was his zeal.