'Certain' in the Bible

For I am certain of this very thing, that he by whom the good work was started in you will make it complete till the day of Jesus Christ:

so that you may learn to recognize and treasure what is excellent [identifying the best, and distinguishing moral differences], and that you may be pure and blameless until the day of Christ [actually living lives that lead others away from sin];

Certain, indeed, even through envy and contention, and certain also through good-will, do preach the Christ;

And being certain of this, I am conscious that I will go on, yes, and go on with you all, for your growth and joy in the faith;