Eliyahu Hanavie

My partner has asked where does the tradition that eliyahu hanavie comes to each seder come from and what has he got to do with the seder night? I can find no source other than a corruption of the minhag to open the door at shefoch chamosecha to show that we are not afraid on the leil shimurim.

Opening the door for Eliyahu expresses our faith in our upcoming redemption (predicted for the month of Nisan) that will be heralded by the reappearance of Eliyahu.The custom is mentioned in Aruch HaShulchan Orach Chayyim 480 and similar customs involving the expectation of the final redemption are cited in the Maharil,Shulchan Aruch HaRav and Chok Yaakov. The Divrei Negidim on the Haggada writes that the reason we open the door not at the beginning of the seder (as would be expected if the only reason were that we are not afraid) is because of the allusion to Eliahu.