"Paddy ... join with your protestant brother." "Your foes have long prided to see you divided." If together, your foes won't oppose you. "Then your rights will be granted"; "keep asunder ... you shall live and die slaves"
This is one of those sadly ironic songs: Most of the early Irish agitation for independence was led by Protestants (e.g. Wolfe Tone was Protestant). Their attempts at rebellion failed in no small part because the Catholic peasantry was indifferent. (Understandably, since their problems were with landlords; the English government had no direct impact on their hardscrabble lives).
If Moylan's dating is right, though, by the time this was written, the situation had changed. By the late nineteenth century, Britain would have been willing to grant Home Rule in some form -- but the idea always died due to the opposition of Irish Protestants, especially in Ulster. Those people, once at the heart of the rebellion, had by then started to cling to Britain as protection for their rights. - RBW