It were endless to dispute upon everything that is disputable.

Penn’s line cautions against the temptation to treat every arguable point as worth arguing. Because human language, evidence, and motives leave almost any claim open to challenge, a life devoted to disputation becomes “endless” and ultimately unproductive. The remark reflects a practical, peace-seeking temperament often associated with Quaker thought: prioritize what is morally and spiritually necessary, and avoid contentiousness for its own sake. It also implies an epistemic humility—recognizing limits to certainty—and a moral discipline in conversation: choose disputes that clarify truth or promote justice, rather than those that merely display cleverness or inflame division.