Hillel the Elder used to take the Pesach, Matza, and Marror, roll them together to commemorate the verse 'with Matza and Marror you should eat it. That is called Korech, a sandwich.
The bitter marror; the marror of pain and suffering; the marror of hardship is sandwiched by the tasty paschal lamb and the crunchy Matza.
This message of the sandwich can reflect a truism of our own expressions to God in prayer.
Depending on how one couches the emotion, one's true feelings become clear.
The final psalm of Hallel, indeed the culmination is reached in psalm 118. Yet, if we were to analyze the torso of the psalm, verses 5-18, the bulk of the mizmor, all remind us of the 'marror' experience in the psalmists life: "from the straits I call out to God", "no fear, God will help, I will see my enemies", "encircled by my enemies" (four times in three successive verses!), "I will not fall, I will not die".
However, due to it being sandwiched beginning and ending by genuine praise, thankfulness and joy, we can only surmise that the psalm emits the totality of the author's expression. The inclusio is heightened by the repetition of the verse as the prologue and epilogue: Hodu LaHashem ki tov, ki le'olam chasdo--Be thankful for God's absolute good, His eternal kindness.
A fitting ending for the expression of praise and joy to God on the holiday of Pesach as it too reminds us that though the embittered experience of the slave consumed our people for generations, the spark of redemption, the emergence from the fire, the worthiness of miracles, the journeying together towards a brighter future--they are what ultimately resonate in our hearts and minds (and taste-buds) this Pesach.
Chag (korech) Sameach!