Psalm 27

Rabbi Richard Levy recounts how when he and fifteen colleagues were jailed in St. Augustine, Florida for protesting the city’s discrimination practices during June of 1964, the Reverend Martin Luther King read to them Psalm 27 to buoy their spirits: “Adonai is my light and my deliverance; from whom shall I be afraid…”
Our sages chose this specific Psalm as a twice daily reading for the entire month of Elul. This Psalm never mentions repentance, as do others. Why did the Rabbi’s choose only this Psalm, along with the hearing of the Shofar blasts, as the preparation for a new year?