From Halopedia, the Halo wiki
Halo Reborn is the twenty-second track (Disc 2 Track 7) included in Halo 3: Original Soundtrack, and plays in the Halo 3 campaign level Halo. It is composed of Halo Reborn (0:00-2:46) and Guilt and Punishment (2:46-3:59).
Halo Reborn (2:46) begins with mournful vocals accompanied by some minor electronic sounds. The vocals sing the melody of Under Cover of Night (from Halo: Original Soundtrack). The first section plays in the opening cutscene as John-117, Cortana, and Thel 'Vadam travel to Installation 08, and continues into the opening gameplay sequence in the snowy canyon. It also plays in Halo: Last One Standing when S. Hartley acquires John-117's signal. The piece made a short reprise in in the track Reborn Relic in Finale (from Halo 3: ODST Original Soundtrack). In the second section, strings take over and build tension as vocals join in the background. The digital notes from the track Infiltrate return in a reprise, but accompanied with a much more prominent percussion accompaniment. The piece fades out quickly. This section plays when Flood combat forms arrive on the installation in Flood dispersal pods.
Guilt and Punishment (1:13) takes over with an eerie ambiance and digital chimes before being joined by the intense, electrically-generated siren-like sounds from the track Shadows (from Halo: Original Soundtrack). The piece ends abruptly on a jarring violin chord. The ambiance plays when John-117, 'Vadam, and Avery Johnson enter the control room, and continues into the cutscene in which 343 Guilty Spark attacks the trio. The following siren-like sounds play during the gameplay sequence in which John-117 battles 343 Guilty Spark, with the jarring chord playing when John-117 lands the killing blow on Spark.