1Therefore we must pay much closer attention to what we have heard, lest we drift away from it. 2For since the message declared by angels proved to be reliable, and every transgression or disobedience received a just retribution, 3 how shall we escape if we neglect such a great salvation? It was declared at first by the Lord, and it was attested to us by those who heard, 4 while God also bore witness by signs and wonders and various miracles and by gifts of the Holy Spirit distributed according to his will.
In these verses we are encouraged to pay close attention to what we have heard - namely the character and work of Jesus described in chapter 1. Matthew Henry says the "Our minds and memories are like a leaky vessel, they do not, without much care, retain what is poured into them", which is why we need to pay close attention. God has revealed Himself to us through the law and prophets (message delivered by angels) and through the gospels and letters ("those who heard"), confirmed by signs/wonders/miracles/gifts and work of the Holy Spirit. There is nothing more important than this message - the gospel - who God is and what He's done. So pay close attention to to it. Read it, study it, pray it, pray about it, talk about it, listen to what others have to say about it, write about it, think about it, meditate on it, ask the Holy Spirit to write it on your heart