本文探討宗教交談中學者所提的「百川歸海」譬喻，以及證嚴法師所歸結的類似說法「宗教如大海」，在慈濟國際救援宗教合作經驗中展現何種涵義，其呼應當今宗教共同促進人類福祉的倫理需求上有何特色。研究資料為證嚴法師的言論，慈濟刊物的海外援助報導，以及筆者在印尼和南非的實際田野觀察訪談。研究發現，慈濟不傳教的人道救援，證嚴法師教化強調尊重在地宗教與文化，志工不為私己的服務行動，對災民長期關懷，且宣揚人人皆可為善助人，是其在許多不同宗教信仰地區被接納，甚至吸引其他宗教信徒加入志工行列的原因，慈濟也提供他們信念實踐的機會。本文顯示，苦難形成宗教合作的契機，喚起各宗教崇尚的愛與慈悲精神，一種深刻的宗教交談來自面對天災時的共同行動。慈濟的跨宗教合作經驗對「百川歸海」的譬喻提供三種詮釋，包括人心歸向和實踐「大愛」的潛能和作為、宗教包容他者的胸襟，以及宗教對全球苦難的首要關懷，其形成開放性的行善場域，帶動受助者成為助人者，集結不同宗教信徒，發展出行動取向的宗教合作模式。

This paper examines the meanings of the metaphor ”all streams go to the sea,” drawn by scholars for the prospect of inter-religious cooperation, and of the metaphor ”religion is like the sea” similarly raised by Master Cheng Yen, in Tzu Chi's international relief that engages people of different religious backgrounds in volunteer work. The study aims to generalize the features of Tzu Chi's experiences in echoing the ethnical obligations of modern religions to enhance human welfare. Research data is based on Master Cheng Yen's talks, reports on international relief in Tzu Chi publications, and field studies in Indonesia and South Africa by the author. The research finds that Tzu Chi's humanitarian aid without proselytizing, Master Cheng Yen's instruction on respecting local religions and cultures, Tzu Chi volunteers' altruistic help for the needy, and Tzu Chi's values viewing everyone as potential helpers, explain the reasons why Tzu Chi has been accepted in different religious/cultural areas, and furthermore recruits many local residents to join its services. Tzu Chi also provides them with chances and resources to implement their beliefs. This paper illustrates that sufferings create opportunities for inter-religious cooperation, since they inspire the high spirit of love and compassion pursued by religions. Joint actions to cope with calamities result in a deep dialogue between religions. Tzu Chi's experiences of inter-religious cooperation offer three explanations for the metaphor ”all streams go to the sea;” that is, human potentials to carry out ”great love,” accommodating other religions, and all religions' imperative concern for global sufferings. Tzu Chi has set up an action-oriented model for religious cooperation by offering an open space for ”doing good” that incorporates believers of different religions.