What glorious riches are here! God has given us everything that pertains to life and godliness. Nothing is left for us to add, on one hand. On the other hand, we are to work hard to add to our faith . . . so that we will be neither barren or unfruitful.
The coming of Christ is a theme that motivates both with accountability and hope.
Peter establishes a level of authority -- we have the word made more certain -- we were eye witnesses. He's not making this up!