"...He bought a nice blue suit with the money he could find
A beautiful way of saying "I'm buying this suit, and dammit, if I can't find anywhere to wear it; I'll get married or buried in it" (I can't count the number of times I've purchased bicycle shorts using that same justification) the lyric references St. Peter.
The original "Rock" (That's what Peter means in Greek) St. Peter was one of the 12 apostles of Jesus Christ. This particular group of 12 are still counted amongst the most famous and revered of the non-dancing boy (in the biblical sense) bands.
In Matthew 16:17-19, Matthew remarks that Peter "will receive the keys to the kingdom of Heaven." Wikipedia reveals that this is the source of popular tales which place St. Peter as the gate keeper to paradise.
"...Well the medicine man started seeing red."
"Medicine men" was the label given Native healers and doctors by Jesuit missionaries who were attempting to Christianize and colonize Canadian Natives during the 17th century. The term was used derisively and descriptively. The missionaries felt that medical science, and all healing in general, was derived from God and therefore unattainable to these men who could not properly be called doctors.
As disease, brought by the Europeans, began to decimate their ranks, the medicine men began to view the Jesuit priests with suspicion. Unaware that it was the germs on the breath and in the robes of the missionaries that was killing their children, the medicine men began blaming the baptismal ceremony itself. They pleaded with Native mothers to refrain from going through with the ritual, and eventually created a rift between the missionaries and medicine men of New France.