'Certain' in the Bible

Having in mind your true faith, which first was in your mother's mother Lois, and in your mother Eunice, and, I am certain, is now in you.

And for which I undergo these things: but I have no feeling of shame. For I have knowledge of him in whom I have faith, and I am certain that he is able to keep that which I have given into his care till that day.

But be certain of this, that in the last days times of trouble will come.

But see that you keep to the teaching you have been given and the things of which you are certain, conscious of who has been your teacher;