Bareil began his monastic life as a gardener, and would have been content to remain one, but his popularity was such that he eventually became a vedek.
Bareil at first chose not to involve himself, lest it hurt his chances of becoming Kai, but after the DS9 schoolroom was bombed, he had a change of heart and came to the station to call for reconciliation.
Bareil, wanting to stay functional so he could continue to advise Winn, directed Bashir to treat him with an experimental drug, vasokin; but while the drug increased the blood flow, it also damaged Bareil's organs one by one, as fast as they could be replaced.