Lowering the wall

​All of the walls surrounding Har Habayis were built very tall with the exception of the wall above the gate on the Eastern wall which was built lower than the others. Why?
A person who became impure through contact with the dead could only be purified with the ashes of the Parah Adumah. The Parah Adumah was slaughtered and burned on Har Hazeisim to the East of the Beis Hamikdash.
Even though the Parah Adumah had to be slaughtered and burned outside of Yerushalaim on Har Hazeisim, the Kohen had to face and be able to see the doorway of the Heichal. The Eastern wall was built lower to give the Kohen an unobscured view all the way into the Kodesh.  
Spiritual death is disconnection from Hashem – the source of life. The Kohen leaving the Beis Hamikdash to prepare the Parah Adumah represents the sacrifice of leaving one’s own spiritual comforts to bring purity to those who need it. 
When a person leaves their environment of holiness for the purpose of connecting others to Hashem, it may seem that they are moving away. In truth, Hashem lowers all of the walls and barriers, giving us unhindered access to the deepest levels of connection.
Sources:
Middos 2:4
Rambam Hilchos Beis Habechira 6:5