If you give someone an assurance that something is true or will happen, you say that it is definitely true or will definitely happen, in order to make them feel less worried.
双语例句
例： He would like an assurance that other forces will not move into the territory that his forces vacate.
他想要其他部队保证不进入其部队撤出的那片领地。
例： He will have been pleased by Marshal Yazov's assurance of the armed forces' loyalty.
他一定会对亚佐夫元帅作出的有关军队忠诚度的保证感到满意。