Take a look at verses 10-12:
10 Concerning this salvation, the prophets who prophesied about the grace that was to be yours searched and inquired carefully,
11 inquiring what person or time the Spirit of Christ in them was indicating when he predicted the sufferings of Christ and the subsequent glories.
12 It was revealed to them that they were serving not themselves but you, in the things that have now been announced to you through those who preached the good news to you by the Holy Spirit sent from heaven, things into which angels long to look.
In other words, this passage teaches that the Spirit revealed to the prophets that their writings were intended for Peter's audience. Granted, their oral messages had an ancient audience of Israelites. Those messages had a specific historical intent. I believe, and the 1 Peter passage seems to agree, that the prophetic books that became part of the canon carried an authorial intent that was distinct from the message God intended the prophets to deliver to ancient Israel. This distinct intent would be a message for the NT church. (Dare I say New Covenant believers?) More on this later when I talk about my class on Old Testament Theology with John Sailhamer. The big idea is that the Spirit intended the writings of the prophets to be used by the church. I can't remember that I've ever heard anyone in my background deal with this passage thoroughly. Am I missing something here?