And it is explained that due to the jealousy of the brothers over the coat of many colors that Jacob gave to Joseph, the sale of Joseph was caused, leading to our ancestors' descent into Egypt. It can be interpreted that the Midrash brought by Rashi is hinted at in the word 'karpas' (כרפס), since 'kar' (כר) is related to the word 'purchase' (קניה) (Genesis 50:1), and it also shares letters with 'sold' (מכר). Thus, it is hinted here that the 'kar', i.e., the sale, was caused because of the 'pas', meaning the coat of many colors.

Similarly, it is written in the book Ben Ish Chai (First Year, Parashat Tzav, Section 32): "This first dipping, which is karpas in vinegar, is a reminder of the cause of the difficulty of the enslavement, which was due to the sale of the righteous Joseph, peace be upon him, and that they dipped his coat of many colors in blood, sold him, and caused sorrow to our forefather Jacob, peace be upon him. This is hinted at in the word 'karpas', where the letters 'kar' (כר) are the end of 'sold' (מכר), and the letters 'pas' (פס) are the beginning of 'coat of many colors' (פסים)."

According to all this, it is understood why we begin the Passover Seder with dipping the karpas in salt water, as it hints at the initial cause of the exile in Egypt.