for和of的一个区别问题

To fullfill one`s duty according to the rules is necessary "for "governance by law.
首先拆句.
(To fullfill one`s duty according to the rules) is necessary for governance by law.
也就是
It is necessary for governance by law.
It=To fullfill one`s duty according to the rules

所以。这儿只能用for。不能也没有necessary of这种表达方法，从意思和句式上都不可以

To fullfill one`s duty according to the rules is necessary "for "governance by law.
你要看意思的。
Sth is necessary for sth.
对什么什么来说是重要的。
怎么可以用OF呢，。OF一般来说是所属关系介词