The pasuk states (Shemos 13:9): ‘So that the Torah of Hashem should be in your mouth.’ The Izhbitzer Rebbe zy’a (Mei Hashiloach, Parshas Bo) explains that on the first night of Pesach, Hashem commands us to purify our mouths through eating matzohs and drinking the four cups of wine. By doing so, our mouths become sanctified for the entire year and we are granted protection from inadvertently placing anything forbidden into them. We also recite the story of yetzias Mitzrayim, which sanctifies our mouths as far as the words we speak. Once we say over the story of the exodus, our mouths become protected from forbidden speech. Accordingly, the pasuk is saying that the Torah of Hashem will be in our mouths and those words will make our mouths holy and protected from sin.
The Me’or Vashemesh writes that this is why this holiday is known as ‘Pesach’, which can be read as ‘peh sach’, the mouth speaks, as we use our mouths on this day to make our words holy and to protect ourselves from anything forbidden going in or out of our mouths.
He continues by saying that eating matzoh is a remedy that protects every Jew all year round from eating anything that is ‘chometz for the soul.’ The holiness of the matzoh protects us from imbibing anything that could damage the neshama.
In this vein, the She’eris Menachem of Vishiva zy’a explained the simanim of the Seder as follows: ‘Kadesh Urchatz’ – if you want to make yourself holy and wash away your sins. ‘Karpas’ – the letters of this word are an acronym for ‘klal rishon peh sasum’, the first rule is to close your mouth. However: ‘Yachatz Magid’ – when there is something that you must say, you should cut it in half.