Where did the traditions from the seder meal employed during Passover come from?
Obviously, the Torah itself issues some specific commands concerning the observance of the Passover. There were some specific commandments relating to the first Passover, the deliverance from Egypt, which included slaughtering a lamb and spreading its blood upon the doorposts of the house, and eating the meal in haste, as the Ancient Israelites were preparing to leave (Exodus 12). Passover or Pesach is codified as one of the appointed times in Leviticus 23, and regulations on how to observe it in the Promised Land are detailed in Numbers 9.
Between the first Passover in Egypt to the Passovers kept in the Land of Israel, coupled with the division and dispersion of Israel, and later with a vast Diaspora Jewish community by the time of Yeshua, the celebration of Passover developed substantially. By the time of Yeshua, the specific order of service for Passover became codified in the Haggadah of Passover, first referred to in the Mishnah. This was focused around a midrashic interpretation of Deuteronomy 26:5-9, which allowed for one to recline and remember the mighty deeds God performed before the Egyptians in delivering Israel:
“You shall answer and say before the LORD your God, ‘My father was a wandering Aramean, and he went down to Egypt and sojourned there, few in number; but there he became a great, mighty and populous nation. And the Egyptians treated us harshly and afflicted us, and imposed hard labor on us. Then we cried to the LORD, the God of our fathers, and the LORD heard our voice and saw our affliction and our toil and our oppression; and the LORD brought us out of Egypt with a mighty hand and an outstretched arm and with great terror and with signs and wonders; and He has brought us to this place and has given us this land, a land flowing with milk and honey.”
We see elements of the traditional Jewish Passover of the First Century included in Yeshua’s Last Supper, and some slight deviations. The Dictionary of Judaism in the Biblical Period summarizes the central elements of Passover contained in the Haggadah:
“The ritual found in the Haggadah is first referred to in M. Pesaḥim, chapter 10, which describes a festival meal marked by a set order of foods and a required liturgy (seder). At the heart of the meal is an explanation of the significance of three foods (unleavened bread, bitter herbs, and the passover offering) and the recitation of the Hallel-psalms. In early Amoraic times, this basic ceremony was embellished through the addition of a discussion of Israelite history, leading up to and including captivity in Egypt. In later developments, continuing to the present, liturgical poems and other homilies have been added to the basic format set in talmudic times.”
Today, we obviously see a wide variation of Passover customs and traditions present in the Jewish community and in Messianic Judaism. There are significant variations between Sephardic and Ashkenazic Jews, as well as between Orthodox, Conservative, and Reform (or Progressive) Judaism. The Passover haggadah is something that has been adapted and changed by each denomination of Judaism, as some haggadahs include an all-night service, where one stays awake and focuses on certain Scriptures, to those that are only focused around a meal at one’s home with family and close friends. There are traditions present in Passover today that are unique to the lands where the Jewish people have been scattered.
Messianic Judaism has adapted many of these traditions to form its own Passover haggadahs, which demonstrate how we are to rejoice in God delivering Israel from Egypt, and Yeshua delivering us from the bondage of sin.
 “Haggadah of Passover,” in Dictionary of Judaism in the Biblical Period, pp 266-267.