'Certain' in the Bible

For this reason, my brothers, take all the more care to make your selection and approval certain; for if you do these things you will never have a fall:

And so the words of the prophets are made more certain; and it is well for you to give attention to them as to a light shining in a dark place, till the dawn comes and the morning star is seen in your hearts;

And be certain that the long waiting of the Lord is for salvation; even as our brother Paul has said in his letters to you, from the wisdom which was given to him;