In plain words
All have risen from the Ātma. When a man recognises this truth, he becomes free of true saṅkalpa; he alone is the embodiment of Śānti. What is Śānti? However many hardships come, however many sorrows come, whatever troubles arise, the one who endures them, bears them, withstands them, pushes through them and goes forward is not one who has experienced Śānti. We must not brood over either happiness or sorrow. As passing as happiness is, just so passing is sorrow. As passing as the night is, just so passing is the day. Each one is only a cloud drifting by. These too are not real. If today you rejoice that it is the full moon, tomorrow the new moon comes. Both are passing. That is why: Anityam asukham lokam. This world is impermanent and without happiness. Who enjoys lasting happiness? Who enjoys lasting Ānanda? If there is joy this minute, sorrow comes the next. Śānti must rise from within us; it is not something that comes from outside.
Every man: I want Śānti. Ask a foreigner what he wants and he says, I want peace. I want peace: three words. I: ego. Want: desire; remove these two, and peace comes. Peace is right behind us, right beside us, right at home with us. Peace is within us. The whole world is pieces.
You are the embodiment of peace You are the embodiment of Truth You are the embodiment of Love You are the embodiment of GOD.
When we recognise that truth, that itself is Śānti.
In Vedānta they have taught three: ādibhautika, ādidaivika and ādhyātmika. Ādibhautika is the body. Ādidaivika is Manas. Ādhyātmika is the principle of the Ātma. This is what is meant by The one you think you are the one others think you are, the one you really are. You are not one person but three. What you take yourself to be is the measure of the body. You are not the body. Nor Manas. You are the Ātma itself. So it is the principle that experiences the knowledge of the Ātma, the Ānanda of the Ātma and the sacrifice of the self that is the true svabhāva. That is the Haṃsa Gāyatrī.