What does the incident with Dev's Udyapan ceremony reveal about Sai Baba's omniscience and his commitment to his promises?

This incident powerfully demonstrates both qualities. As detailed in Chapter 40, when Jog brought Dev's letter of complaint, Baba showed his omniscience by stating, "When the letter is opened before Me, the state of mind within the letter is already known and stands before Me in person." He knew Dev's feelings without needing to read the words. Regarding his commitment, Baba meticulously explained how he kept his promise by appearing in the guise of a Sanyasi with two others, exactly as he'd mentioned. His unwavering dedication to his word is captured in his powerful declaration: "Look, for the sake of My word, I would die; but the words from My mouth shall never be otherwise." This showed that his promises are always fulfilled, though not always in the way devotees expect.