So say we all
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So say we all is analogous to the Christian "amen" (which itself means "so be it" or "so let it be").
"So say we all" is said at the closing of prayers, akin to "amen". (Miniseries) However, the word "amen" is still attested in the Colonial language (Resurrection Ship, Part II) and is used to end prayers in some circumstances (Lay Down Your Burdens, Part II).