The writer of so-called "Hebrews" says that in the early days God spoke through the prophets but "in these last days has spoken to us in His Son" (Heb 1:1,2).
He continues: "For this reason we must pay much closer attention to what we have heard so that we do not drift away from it" (Heb 2:1)
For what reason?
The reason that God has now sent His Son to speak to us. "Ignore Him at your peril" the writer is basically saying:
"How shall we escape if we neglect so great a salvation?" (Heb 2:3).
How indeed. The implied answer is "we won't".
There are a number of important lessons here:
Firstly, that its POSSIBLE for Christians to lose what they have. So much for "once saved, always saved" according to this passage!
Secondly, notice that this perilous state is arrived at GRADUALLY. We "drift" away. The trouble with drifting is you often don't notice its happening until you're in serious strife.
Thirdly, notice the cure for the problem: "We must pay much closer attention to what we have heard [so that we do not drift away]"