One Final Effort
From Halopedia, the Halo wiki
The piece begins with a low strings note, which is followed by the piano playing the five-note E Dorian melody (from the later track Finish the Fight) and two variations of the phrase to answer the melody as percussion joins in. Single piano notes and high strings slowly build in tension, and the piano breaks into a more prominent rendition of its part from Unyielding (in Halo 2: Original Soundtrack). High strings join in with a rearrangement of the third section of the track Truth and Reconciliation Suite (itself a variation of the Halo Theme). The piano accompanies the melody throughout, and takes over the low strings ending with the five-note E Dorian melody. A full rearrangement of the original Truth and Reconciliation Suite section was featured in the later track Greatest Journey, which was played in the final level of Halo 3. That version also uses the iconic choir chant used for the main menu, during the piano climax when the theme is in full swing.