'Sure' in the Bible

but in every nation the person who fears God and does what is right [by seeking Him] is acceptable and welcomed by Him.

When Peter came to his senses, he said, “Now I know for certain that the Lord has sent His angel and has rescued me from the hand of Herod and from all that the Jewish people were expecting [to do to me].”

And [as for the fact] that He raised Him from the dead, never again to return to decay [in the grave], He has spoken in this way: ‘I will give you the holy and sure blessings of David [those blessings and mercies that were promised to him].’