Whoever breaks the law will be punished sooner or later.

主语从句
whoever“无论谁”,可以引导主语从句
它即是breaks the law的主格 又是be punished的主语
主语从句有以下几种类型
1.常规主语从句,即句子在复合句中充当一个主语,比如
（1）That he finished writing the composition in such a short time surprised us all.
（2）Whether we will go for an outing tomorrow remains unknown.
（3）Who will be our monitor has't been decided yet.
2.为了防止句子头重脚轻,通常把形式主语it放在主语位置,真正主语搁置于句末,比如
（1）It is certain that he will win the match.
（2）It is true that he has made a very important discovery in chemistry.
（3）It is very likely that they will hold a meeting.
这个句子属于第一类型
关于主从还有以下几点总结:
引导主语从句连词有that,whether,who,what,whatever等
连词位于句首不能省略
主语从句大多数情况下视为单三,但也有例外
以that 引出的主语从句,常以形式主语it引导.
It is +形容词/名词/某些动词ed + that 从句.
在有些that从句中要用虚拟语气

不论什么人犯了法，迟早要被处罚的。
whoever breaks the law是主语从句作主语