'Sure' in the Bible

Wherefore the rather, brethren, give diligence to make your calling and election sure: for if ye do these things, ye shall never fall:

We have also a more sure word of prophecy; whereunto ye do well that ye take heed, as unto a light that shineth in a dark place, until the day dawn, and the day star arise in your hearts:

then [in light of the fact that all this is true, be sure that] the Lord knows how to rescue the godly from trial, and how to keep the unrighteous under punishment until the day of judgment,