The song is an ancient dirge sung at wakes that tells of a soul's travel through dangers from earth to purgatory. "The safety and comfort of the soul in faring over the hazards it faces in the afterlife, are in the old ballad made contingent on the dead person's willingness in life to participate in charity." Sometimes a good heart is enough to get you through life...
The article has a lot more details about the full lyrics and what certain lines mean. I thought it was interesting how it applied to Richard, doing the hero's journey, going underground to emerge in the light at the end, changed. A soul going through hazards in the underworld.
It is a Christian song, but it has lots of pagan imagery, so it has a very primal, ancient feel.
Here is a translation of the whole song (lyrics mention a Bridge of Dread!): http://www.duntemann.com/likewakepage.htm
More information: http://en.wikipedia.org/wiki/Lyke-Wake_Dirge