my opinion on rahao is, separation of the above from the below. sometimes there are two or three rahao one after the other. it is just show the significance of the rahao tuk. in general the entire gurbani has the same theme, because of that we the readers think that the bottom part of the paragraph is explanation of the above. rahao separates the the stanza above or even two from the the gurbani below. the rahao tuk has special meaning that is why it is separated from the rest of the paragraph.