At the conclusion of the delicious meal, after grace has been recited, a fifth Kiddush cup of wine is poured and placed at the center of the table. The front door to the home is then opened, and another prayer is recited as everyone waits for the prophet Elijah to enter and take a sip from his cup.1
The opening of the door is a reminder that G-d protected the Jews from the plague that slew all the Egyptian firstborn during the night of the first Seder. Therefore, opening the door expresses our trust in G-d’s protection.2
It is also of note that Elijah is the one who visits the circumcision ceremony of every Jewish male child and testifies that Jews are scrupulous regarding the practice of circumcision. This is significant because according to the Talmud, males were only able to eat from the paschal lamb if they were circumcised. So, in effect, Elijah comes to the Seder to “testify” that all males present are circumcised.3
This welcoming of Elijah is the second half of the Seder. While the first half is the commemoration of the exodus from Egypt, this second is an allusion to the forthcoming arrival of the messiah that will be announced by Elijah.4