Reading Peter’s letters is quite different than reading Paul’s. Paul was a scholar trained in biblical academics, which involves focusing in on meaning. It usually means looking at something with a microscope in order to clarify what sometimes appears to be minutia. Peter, who came to Christ as an uneducated fisherman (though he most certainly did not remain so), turns the microscope around, which turns it into a telescope.
So, while Paul is often focused on the inner, personal realities of faithfulness, Peter is focused on the grand scheme of Christ’s mission in the world. Where Paul was focused on particulars, Peter was focused on the whole. While understanding Paul involves the personal experience of the Holy Spirit through regeneration, understanding Peter builds on regeneration and takes in the whole sweep of human history in the light of Christ. Peter understood history as the Old Testament. He had nor needed any other history book. As such, reading Peter without more than a passing familiarity with the Old Testament will surely lead you astray. Peter brought his ordinary understanding and experience of Jesus Christ to the Old Testament and built upon it. In Paul’s writing we find history brought to faithfulness, while in Peter’s writings we find faithfulness brought to history. Paul was focused microscopically, while Peter was focused macroscopically. So, while reading Paul clarifies the details, reading Peter magnifies the vastness of Christ’s mission to the world.