The 3rd and the 4th night is for strengthening the Anahat chakra. On these 2 days, we should recite the Kavach of the Devi.
If you want to read the original version of the Kavach of the Devi (which is in Sanskrit), please go here.
Let me share my experience of reading the Kavach of the Devi.
Usually, I will read the English translation. But ever since coming back from Vashi, I was told that reading the Sanskrit words have a bigger effect on our subtle system. So, I tried with my inaccurate pronunciation, stumbling here and there, tongue twisted, I could feel clearing going on as I was reading. The Sahasrara was emitting cool vibrations but the body was just emitting heat. It's as if the chakras were trying to aligned themselves to their own natural speed and therefore, emitting heat from the friction.
My husband reads the Chinese version. Not sure whether the effects is the same though. Sometimes I joked with him and said the Deities can't understand Chinese, maybe he should start reading in English instead (in the hope that he will faster improve his English). All Deities understand Universal language anyway. He! he!