These excerpts derive from the end of the retelling of the Exodus story and the recitation of Psalms 113 and 114 (Hallel, which begins here with the words “We say before him” and ends with the words “a spring of water”) prior to the consumption of the festive meal.
[Accordingly w]e are bound to thank, praise, laud, glorify, exalt, magnify, immortalise in song Him who lives fore[ver. Migh]ty Saviour, the Worker …