The purpose of what we say in our prayers is as follows. The thanksgiving is in recognition of our incapacity to offer thanksgiving as we should at this present moment, of our negligence in doing so at other times, and of the fact that the present moment is a gift of God's grace.
The prayers offered by the monks in Peter's day always began with a thanksgiving. This thanksgiving, according to Peter, was not so much a genuine fulfillment of humanity's duty to be grateful to God. In fact, it functioned first and foremost as a reminder that people cannot be truly thankful as they should. Whether it be sin or merely ignorance that prevents people from truly recognizing all that God does for His children, the gratitude offered God is never sufficient. It overlooks things that God has done and continues to do. Even if humanity were able to recognize every grace conferred to humanity, people could still not thank God adequately since every moment it would be necessary to thank God merely for the gift of being itself.
Peter recognizes that beneath every thanksgiving offered to God should be implicit remorse and recognition that it is never enough. Do we deceive ourselves into believing our gratitude is sufficient?