The mind.  Those who do Sat Naam Simran in their Surat becomes Sat.  When Sat Naam goes into Surat or mind then Surat becomes Sat, and as Sat Naam Simran progresses it goes in to other spiritual centers – Sat Sarovars and activates these Sat Sarovars inside the Suksham Dehi.  These seven centers of spiritual energy are contained within our own Suksham Dehi and are illuminated with the Sat Naam and all of our Bajjar Kapaats open up, including the Dassam Duaar and a permanent connection with the Param Jyot is established.  This is how our entire Suksham Dehi and physical body is filled with Amrit and goes in to a stage when our entire body is filled with Amrit and our Rom Rom goes in to Sat Naam – or our Rom Rom becomes Sat.