There is a flow to the opening two chapters of this letter, but they're not easily defined. Of course, it's a letter all about the redemptive priestly ministry of Jesus the Christ, God the Son incarnate. He, as the opening verses of chapter one state, is the ultimate revelation of God. He is God's living, redemptive revelation displayed in "these last days"(1:2). And that means His coming is the conclusion of all God was preparing the world for through the ministry of the prophets in the Old Testament.
That brings us to the first four verses of chapter two. There is grace-filled warning here. There is a great deal at stake in the way we "hear" the revelation we have received in Christ. In other words, this revelation in Christ is not just an event. There is also a necessary response to this real, historic event. If it was dangerous to trifle with previous revelation through law and prophets (and it was - 2:2), it is dreadfully more dangerous to trifle with God's final redemptive revelation in the Christ.
So our writer makes a plea to these Jewish believers - "We must pay much closer attention to what we have heard, lest we drift away from it"(2:1). We studied those words last week. This is a mental inattention, not a denial of doctrinal truth. We're being called to mental focusing. And our writer tells us this kind of spiritual concentration matters - "...how shall we escape if we neglect such a great salvation?..."(2:3). It's a rhetorical question. There is no escape from judgment for the mentally distracted.