'Sure' in the Bible

Never for a moment quail before your antagonists. Your fearlessness will be to them a sure token of impending destruction, but to you it will be a sure token of your salvation--a token coming from God.

Therefore, my dearly-loved friends, as I have always found you obedient, labour earnestly with fear and trembling--not merely as though I were present with you, but much more now since I am absent from you--labour earnestly, I say, to make sure of your own salvation.