Notice this isn't a private feeling — it's a command to speak. “Let the redeemed... tell their story” isn't decoration on top of gratitude; it's the instruction itself. The psalm assumes silence is the default and testimony takes actual effort to produce. It's addressed specifically to “the redeemed” — meaning if you've been rescued, this line was written to you, by name category, not in general. This also opens the entire psalm — meaning everything that follows, storm, chains, desert, exists in service of getting people to actually say what happened, out loud.