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.