ROBERTA, here is my response to your question:

What is the meaning of the PESACH'S (Passover's) SEDER?

Roberta, SEDER (in Hebrew), means ORDER, and applies to the taxonomic way of eating, drinking wine, praying, and singing, the first Passover's night. Yet, it is my belief that it is a reliving of Creation , for Chaos was changed into Order , a sine qua non for human existence. You and I can communicate --for instance-- because we follow a given protocol. Disordered communication results in chaos. At the biological level, genetic disorders derive from wrong genetic information giving rise to defective proteins, And normally configured proteins are the dictators of a normally configured organism. However, modifications of genes (mutations), when resulting in the generation of beneficial new proteins, confer advantages and eventually give way to new, better-suited species.
It had bothered me that light was created after making order, until I realized that there is no sense in seeing disorder.
Order is basic, abstract, absolute. In Plato's sense, it represents a Form (the Idea of Orderliness). Light, in contrast, is concrete, variable in wave and intensity, being 'just a manifestation' of the 'Idea' of Brightness. In fact, the opposite of Darkness --also an Idea-- is Clearness, not Light. Moles don't need light, only order.
Obsession-compulsion is a pathological manifestation of the inborn need for order. It now appears that such condition is related to deficient neurotransmitter production --mainly serotonin and epinephrine-- at neuronal synapses.
Religion is a special manifestation of the inborn need for order. Thus the subtle connection between religion and obsessive-compulsive syndrome. Religiousness has been adjudicated to the presence of specific genes, too.

Once, I was requested to say a few impromptu words during a Bar Mitzvah, in front of many orthodox rabbis and of high-school pupils. Being myself non-religious, I found myself in dire straits. By chance, I had been indulging those days in finding a rational explanation for the Passover Seder, for I found the classic explanation wanting in depth. I felt inspired, and spoke to the congregation in the following vein:

"On the sixth day, after creating Adam from clay, God realized that something was amiss… and it was Adam's helpmate, Eve, whom He proceeded to create, with Adam rib's help. His task appeared to have been now completed. Yet after resting on the seventh day, He felt that the work was not really finished. Something was still wanting… And what was it?
His People, His Chosen People! After all, He had created the world specifically for them, to be a "light unto the nations."
For that purpose, He now delegated His authority by choosing Moses, our Teacher, who was now to become His helper. And God believed that now His task had been truly fulfilled...
But it so happens that lately there is bad blood between Arabs and Jews, and worse still, the Jews are in internecine conflict. Therefore, God will have to delegate again authority to solve this tragic situation…
And who will be now in charge of helping Him, through the effecting of His commandment?
You, youngsters, the new generation in Israel, will be in charge of helping God in this sacred mission!…

You know, Roberta, I was applauded! And later on was told that I had dared to step firmly and successfully where the angels fear to tread --a most amazing feat from the mouth of a non-believer...
I explained, "I detest being a slave, as my ancestors were. It is written in the Talmud that ten measures of beauty God gave to the world, and that Jerusalem got nine of them. I say, human beings received from God a tenth of His intelligence, not to serve and adore Him, but to help Him. I believe that that tenth of intelligence He renounced to, and it is now ours to utilize for helping Him."
I tell you, Roberta, the facial expressions of my interlocutors denounced intense puzzlement; they changed the subject...