The answer is: For his mercy endureth forever

Psalm 136 - This beautiful psalm highlights God's steadfast love, with the refrain "For his mercy endureth forever" emphasizing His unchanging nature. Its use of repetition mirrors ancient Israel's practice of communal worship and remembrance, similar to the celebrations in Exodus 15:21 when Miriam led the women in song after crossing the Red Sea.

Psalm 136 is often described as a hymn of thanksgiving, and its repetitive refrain serves a captivating purpose in worship. By echoing "For his mercy endureth forever," it instills a rhythm that not only uplifts the spirits of the worshippers but also drives home the unwavering commitment of the Divine. This kind of call-and-response format was vital in ancient worship settings and was particularly effective for communal memory, allowing those gathered to reflect deeply on their shared history and experiences.

Interestingly, the structure of Psalm 136 reminds us of the Hebrew poetic style known as parallelism, where themes and ideas are reiterated or balanced against each other, rather akin to how a modern song's verses might return to a catchy chorus. One can draw parallels with the liturgy of various religious traditions today, where iterations serve to reinforce central tenets of faith.

The grand themes of creation and salvation in this psalm denote a characteristic of mercy that isn’t about sentiment alone but indicates a robust, active involvement in the seeking out and caring for humanity. And, did you know that various interpretations connect this "mercy" to the Hebrew word "chesed," which implies a depth of steadfast love and loyalty? In contexts outside the Hebrew Bible, ancient Near Eastern views often saw divine involvement as unpredictable, making the steadfast nature of this depiction especially remarkable—it not only assures trust but provides comfort.