Sentence:  As Conor Cruise O'Brien has pointed out, this passage has a "poignant ring," in light of the probable fact that Burke's father was one of those who betrayed his "duty" by sacrificing his "opinion of eternal happiness" to the <WSD>necessitudes</WSD> of legal practice. 
Meaning of the word marked with <WSD> tags:  A circumstance or event which is necessary or unavoidable, especially because it is a requirement of a social role or natural state of affairs.