To cause (another) to believe or feel sure about something
To render certain
They are sound sleepers, I assure you.
She blinked and read it again, counting the zeros to assure that she had read it properly.
I assure you, I have managed to contact all but three and if I located them I would get down on my knees before them and beg forgiveness, just like I've done with the others .
I must assure myself you are carrying nothing on your person.
I assure you I was his enemy eight years ago.