We don’t know how often this is played at funerals. It is the concluding scene of Gotterdammerung with the voices taken out. It speaks of fire. Gotterdammerung is the last opera in Wagner’s Ring Cycle. You either love or hate Wagner, but you’ve got to admit that from 5 mins in it’s pretty good stuff for a farewell/committal.
The story is too complicated to give you here — look it up. Basically, this lass jumps on a fire and is immolated.
Here is a painting by young American artist Dana Schutz of Brunnhilde throwing herself on the pyre.