Tying our sheep to the bedpost.
The Yetzer Hara is much stronger than us, our only hope is for Hashem to fight him for us. But why would Hashem do such a miracle, especially if we've been sinning and falling for so many years?
Perhaps the answer to this question lies in the story of Yetzias Mitzrayim. The Yidden in Egypt had reached the 49th level of impurity. They had cried out to Hashem in utter powerlessness, and Hashem had heard their cry. But they didn't have any merits of their own. As the Pasuk in Yecheskel (16:6) says: "Ve'at Erom ve'eraya - and you were naked and bare". So in what merit were they able to leave? As the Pasuk continues... "and I passed over you and I saw you wallowing in your blood, and I said to you, in your blood you shall live, and I said to you in your blood you shall live". The Targum Yonosan translates these two bloods as referring to the blood of the Pesach sacrifice and the blood of the Bris Milah that the yidden made before leaving Mitzrayim. So we see that the Yidden did indeed need some Zechusim before they were able to merit Yetziyas Mitzrayim.
Let us try and understand what was unique about these two particular Mitzvos that enabled them to break free from the lowest levels.
Hashem told the Yidden to take a sheep and tie it to the bed post. The Beis Ahron of Karlin writes that the miracle was twofold. Firstly, because the sheep were worshiped by the Egyptians who saw their G-d being tied up as a sacrifice, and yet they didn't say anything. And the second miracle was, quote:
"...that the Yidden themselves did such a thing and gave themselves over with complete Messiras Nefesh for the faith and honor of Hashem. And this could not have been done in any other way, only with Messiras Nefesh. Because from such an abominable and disgusting place (like Mitzrayim) that the yidden were in, as it says "you were naked and bare", they could not have left from there to freedom only through this - that they were Mosser nefesh completely for Hakadosh Baruch Hu. And the Sefarim write that they tied it to the bedpost because that is the place where the strength of the Egyptians came from (sexual promiscuity). And even so, from the very place that the Egyptians took their strength of impurity, the Jewish people tied it there - with Messiras Nefesh for Hashem".
When we train ourselves to give our will and life over to Hashem's care with Messiras Nefesh, in essense, we are figuratively tying our animal nature to the bed post by surrendering our desires to Hashem. In this merit, we are worthy of the miracle that occurs afterwards when Hashem removes us from Mitzrayim and we see - as the Pasuk says: "Hashem Yilachem Lachem, Ve'atem tacharishum - G-d will fight for you, and you shall be silent".
And this is also perhaps why the second blood was the blood of Milah, which again symbolizes the Messiras Nefesh that the Yidden had in guarding the bris and covenant with Hakadosh Baruch Hu.
As the Bne Yissachar writes (Derech Pikudecha): "We have a tradition from our fathers that the Yetzer Hara desires more than anything to attack a person through carnal sins, because in this desire are included all the others".
Since carnal desire encompasses all other desires, by tying the sheep to the bed-post and by making a Bris Millah, both of which symbolize Messiras Nefesh in the area of kedusha, the Yidden were in essence giving ALL their desires over to Hashem, and in this merit they were able to break free of the impurity of Egypt.