necesary 后既可以跟to 也可跟for.
Sleep is necessary to your health.
It is necessary for you to do sh.和it is necessary that you...是一样的,只不过是 用that 句子
后面要用should, 如; It is necessary that he should come early. should 有时省略,但后面一定用原形动词,It is necessary that he come early.不是he comes ealy.