Pesach, Matza & Marror
"Pesach" is called so because Hashem "jumped over the houses of the bnei Yisrael when he smote the Mitzri'im". In Avodas Hashem, "Yisrael" symbolizes our "Aliyos" i.e. where we succeed in serving Hashem, and the Mitzri'im symbolize the Yeridos which occur in between each Aliyah. He explains that Pesach symbolizes how Hashem "Kills" our Yeridos, and jumps over them to gather together all of our "aliyos". He then puts the Aliyos all together, and in the merit of them all, we are zoche to leave Mitzrayim - i.e. the bondage of the "self".
After this he writes as follows:
Therefore, we need to learn from this that a person should never look at his "Yeridos" - that he always falls from his spiritual state, but rather he should look only at his aliyos. And therefore, when he sees that he is in a state of shiflus (degration), he should not despair, but rather strengthen himself above his understanding and go back up. And let him not look at his past and say that "since until now I thought I had already come to an understanding that it's not worthwhile to give in to my selfish desires, and yet I still see that right away I lose this state of mind", if so, a person asks himself, "what is the use of my "aliyos" if each time I go up I need to fall? What do I gain from this?" And the answer is (as the Pasuk says), "and the Jewish people moaned from the difficult labor and their supplications went up to Hashem". This is to say that their "awakening below" brought Hashem to kill the Egyptians, and therefore only the Yisrael were left (i.e. the aliyos), and all the aliyos were gathered together to one big cheshbon, one after another, and through this they had a large vessel to receive the divine blessing (of the redemption)... And from this we see that no good we do is ever lost...
In continuation of this idea, he also writes about the inyan where Hillel used to eat the Korbon Pesach together with the Matza and Maror. Maror symbolizes the bitterness of the struggle with the Yetzer Hara/Self, and Matza is a lashon of "Matzusah" - which means "an argument", i.e. the argument that we have with Hashem when we ask him why he made it so hard for us to let go of the "self". We eat this bitterness (the Marror) and this argument with Hashem (the Matza) - together with the "Pesach" (i.e. the Aliyos and closeness with Hashem - as explained above), because it is only through the bitterness we felt - and the questions that we had about "why it is so hard", that we are zoche in the end to real closeness to Hashem. It is precisely through the difficulties we experienced that we ultimately come to the realization that we cannot do it on our own, and through this, we develop the proper vessels and cry out to Hashem and finally He saves us from the bondage of our "selves".