'Sure' in the Bible

(and our hope for you is sure;) or whether we are encouraged, it is for your encouragement and salvation: knowing that as ye are partakers of the sufferings, so also of the encouragement.

But as you excel in everything -- in faith, in speech, in knowledge, and in all eagerness and in the love from us that is in you -- make sure that you excel in this act of kindness too.

I have thought it absolutely necessary therefore to request these brethren to visit you before I myself come, and to make sure beforehand that the gift of love which you have already promised may be ready as a gift of love, and may not seem to have been something which I have extorted from you.