Peter has just called the attention of his readers to the salvation which they had received and the hope that they had. Not only is this salvation spectacular, it is unique to mankind.
Take a look at this passage in 1 Peter 1:10-11.
Not only is mankind overwhelmed by this great salvation that Christ has obtained for us, but the prophets of old and even angels long to know about this salvation that Peter is describing.
According to this passage, Peter explains how this salvation was of the greatest of interest to the prophets of the Old Testament. Perhaps one of the greatest themes of the Old Testament prophets is the grace that would be revealed when the Messiah came. Peter, along with Paul and several other New Testament writers point to this interest of the prophets multiple times.
Peter describes them as looking intently into the future, longing to know more about this grace and salvation.
The topic of grace is one of the main topics of 1 Peter, and is probably due to the fact that Peter knew just how important this topics was to the Old Testament writers. And if something carries that much weight before it even occurs, it must be worth paying attention to. And that is just what Peter does, along with most of the rest of the New Testament.
Grace is paramount.