Yama chooses death, finds the path to the other world and becomes king of those who follow; the funeral hymn directs the dead to him past his two dogs.
Yama, Vivasvat's son, is a king who went to the heights and found the path for many; the place he found cannot be taken away. One verse says he chose death and gave up his body. The funeral hymn tells the dead man to take the old paths, pass the two dogs of Sarama's brood, meet Yama and the fathers and put on a new body; Yama is asked to entrust him to the dogs, who also roam among the living. Another hymn shows Yama drinking with the gods under a fine-leaved tree, with flute and song.
The funeral book repeats the Rigveda verses and adds that Yama was the first of mortals to die and the first to travel to that world, that Mrityu (Death) is his watchful messenger, and that nothing is seen above him.
What is different here:
States outright that he was the first mortal to die; Death becomes a separate figure serving him.
Narada describes Yama's assembly hall to Yudhishthira: built by Vishvakarma, golden, over a hundred yojanas wide, free of grief, age, hunger and thirst. Royal sages of old, Pandu among them, wait on Yama there, with Time, Death, officers who count each creature's days, and sinners too; Gandharvas and Apsaras fill it with music. Its lord is called king of the fathers and god of justice.
What is different here:
A built hall with a court and record-keepers replaces the tree and pasture; Yama is now named god of justice.
Sources: Hymns of the Rigveda, tr. R. T. H. Griffith (1896), hymns read for the Vedic layer; Hymns of the Atharva-Veda, tr. R. T. H. Griffith (1895); The Mahabharata, tr. K. M. Ganguli (1883-96), sections read for the Vedic layer