Synthesized answer
The central thesis of this text is a move from the distinction between performative utterances and statements to a more general theory of "illocutionary forces" of utterances [1]. Austin initially focused on this distinction, but ultimately abandoned it [1].
This new theory of illocutionary forces has significant implications for a variety of philosophical problems [1]. The provided passage does not offer further details on the specifics of this theory or its broader philosophical bearings beyond stating its existence and importance.
Synthesized from the book passages below. Chat with the book on Feynman for follow-up.
From the book
Title: How to do things with words by J. L. Austin Description: This work sets out Austin's conclusions in the field to which he directed his main efforts for at least the last ten years of his life. Starting from an exhaustive examination of his already well-known distinction between performative utterances and statements, Austin here finally abandons that distinction, replacing it with a more general theory of 'illocutionary forces' of utterances which has important bearings on a wide variety of philosophical problems.