how will we escape [punishment] if we neglect such a great salvation? [For it was] first announced [to people] by the Lord and then confirmed to us [i.e., the writer and other Christians] by those who heard Him [i.e., the original apostles].

Since God wanted to show conclusively to those who would inherit the promise [i.e., Abraham and all of his spiritual descendants], how unchangeable His purpose was, He confirmed it with an oath.