Pesach | Birkat HaShir (1), by Rav Yitzchak Etshalom

Why do we almost finish the Berakhah after Hallel at the Seder - then abruptly switch to Hallel haGadol and Nishmat?

Our common practice is to read the Hallel over the fourth cup of wine, after which we nearly finish the blessing customarily recited after Hallel - but without a "signature" (חתימה). We then recite Psalm 136 and נשמת כל חי which we read to its conclusion - "מלך א-ל חי העולמים". This odd mix of a double-conclusion to Hallel is the result of several confusing sugyot. We assess the sources, including the key rulings of the Geonim and Rishonim and follow them through to today's common practice.