“Therefore we must pay closer attention to what we have heard, so that we do not drift away.”
What was heard was the message spoken by the Lord and preached by the apostles, vv. 2-3. “Must” leaves no alternative. Listen closely. Otherwise, we will fall away.
This is why we emphasize serious Bible reading, study, and memorization. It means spiritual life. What is my plan to pay closer attention to God’s word?