After the conclusion of the Seder, there is a universally accepted custom to pour a cup of wine and open the door.

According to tradition, at this moment our homes are graced by the presence of Elijah the prophet.

Opening the door expresses our trust in G‑d’s protection.

Elijah is alsothe one who visits the circumcision ceremony of every Jewish child, and testifies that the Jewish people are scrupulous regarding themitzvahof circumcision.

haggadah Section: Bareich
Source: The Illustrated Jewish Bible for Children