In 2 Peter 3:15-16, Peter tells his readers "our beloved brother Paul also according to the wisdom given unto him hath written unto you; As also in all his epistles, speaking in them of these things; in which are some things hard to be understood."
Certainly God breathed out some difficult doctrine and scripture through the apostle Paul. Ironically Peter's passage here in 1 Peter 3:18-22 is considered one of the hardest to interpret in all the New Testament. But we know that "all scripture is given by inspiration of God and is profitable" for our lives. So let's strap on our thinking caps and look for the doctrine, reproof, correction and instruction in righteousness that God has for us in this difficult text.