Hebrews 6:4-12 It Is Impossible

Note the warning the writer gives to those who are in danger of falling away from the truth!  How is it possible to “fall away and not be brought back to repentance”?  How can this be prevented?  How do some “crucify the Son of God all over again”?  Why does some land produce “a crop useful” and other land produce only “thorns and thistles”?  What does this mean for us today?  How were the readers to “make their hope sure” (v.11)?  How do we?