Peter continues his quest to reinforce to the brethren that God's word holds all things to "life and godliness" (vs 3). So, he seeks to "remind" (vs 12), "stir" (vs 13), and "make every effort" (vs 15) to stress the importance of God's promises to them so they can "recall" these things when he is gone (vs 15).
These are the words of a faithful disciple of Jesus Christ who knows his days are limited on this earth. With that in mind, he stresses the power of the prophetic Word. All of it is trustworthy. Each writer of the Bible spoke as they were moved by God: