In Hebrews 6 if you continue to read down through the chapter,the writer speaks of thorns and briers whose end is to be burned, in verses6-8.
Thorns and briers is a very common OT. figure for apostates among the covenant people,in ezk2, and Isa.
In verse 9 a clear contrast is given with the "but Beloved" we are persuaded better things of you and things which accompany salvation.
This fits with the context of the chapter,and the whole book itself, as in Chapter 2;9-16 The Lord Jesus redeeming the seed of Abraham,while others in chapter 3,10, 12 , fail to enter into the eternal rest
