1. 动词 “assure” 用来表达 “（为消除疑虑）向……保证”，后面接宾语代词，以表明向谁保证。

I assured him that the package would arrive on time.

She assured me that the work would be done properly.

2. 动词 “ensure” 的意思是 “确保（某事会发生）”，后面不接宾语代词，而是直接说明事件。

I ensured the package arrived on time by delivering it personally.

She ensured the work was done properly by hiring the best workers.

3. 动词 “insure” 的意思则是 “给……上保险”。

I insured my house against fire and burglary.

The sales person advised me to insure my new computer.