We have discussed on a number of occasions the dominance of the theme of praise and thanks in the procedures of seder night. As well, the recurrence of the number 4 – 4 cups, 4 questions, 4 sons, etc –  is also well known. The gemara (Berachos 54b) states that there are four individuals whose situations demand that they give thanks to HaShem: Those who travel by sea and reach their destination, those who traverse a desert safely, those who emerge from captivity and those who survive an illness. In the times of the beis hamikdash, this thanks would be expressed in the form of a korban todah which was just discussed in last week's parsha. Today, one makes birkas hagomel in the presence of a minyan. The Shulchan Aruch (OC 219:1) provides a mnemonic for this foursome: “vechol hachayim yoducha selah.” The word ×—יים  stands for ×—ולה, ×™×¡×•×¨×™×, ×™×, ×ž×“בר.

If we examine the yetzias Mitzrayim experience as a whole, from the very beginning to its ultimate culmination with the entry into Eretz Yisrael and building the beis hamikdash, we find that HaShem's great salvation covered all four of these situations. First, we broke free from centuries-long captivity in Mitzrayim. We were led through the Yam Suf to safety. We were protected through decades of travel in the desert. Although we were not stricken with serious illness (unless you consider the magaifos in the desert,) we certainly find that the Egyptians were inflicted with possibly hundreds of maladies from which we were spared. As well, the midrash (Tanchuma Yisro 8) recounts that all blemishes and disabilities were healed at Har Sinai. With this perspective, our feelings of gratitude and thanks on seder night are all the more intensified. 

I have heard that the source for this thought is the Vilna Gaon.

Have a chag kasher ve'sameiach and a good Shabbos!