'Confirmed' in the Bible

how will we escape [the penalty] if we ignore such a great salvation [the gospel, the new covenant]? For it was spoken at first by the Lord, and it was confirmed to us and proved authentic by those who personally heard [Him speak],

(for those Levites who formerly became priests [received their office] without [its being confirmed by the taking of] an oath, but this One [was designated] with an oath through the One who said to Him,“The Lord has swornAnd will not change His mind or regret it,‘You (Christ) are a Priest forever’”).