What he is when he first sets, that is the nidhana. On it the fathers are dependent Therefore they put them down (nidadhati), for they share the nidhana of that Sâman. Thus a man meditates on the sevenfold Sâman as the sun.

In plain words: The setting sun is the ending part of the chant, and the ancestors who have died belong to it. That is why people lay down offerings for them. This is how to meditate on the seven-part chant as the sun.