“You are perfectly unaffected by all expressions of lack of love. These can be either from yourself and others, or from yourself to others, or from others to you. Peace is an attribute in you. You cannot find it outside. All mental illness is some form of external searching. Mental health is inner peace. It enables you to remain unshaken by lack of love from without, and capable, through your own miracles, of correcting the external conditions which proceed from lack of love in others.” (ACIM, COA ed.,T-2.I.26:1-7)
This person that Jesus is talking about in this quotation is the “real” “you,” the Self, the Christ-Self. Our personality, while it is egoic, does react to lacks of love, but all of this is not truly real. Our mental health for the Self gives us only peace. And it is this we can experience when we don’t get stuck in the egoic self, for this self is actually mentally ill (to use Jesus’ terms in this quotation).
Jesus refers to the insanity of the ego in other places in A Course in Miracles. We can never, never, expect to be mentally healthy until we have dislodged the ego, and dislodging the ego is a major goal of ACIM. When the egoic self is gone, we are free to let the Christ-Self emerge from the depths. Once this Self has learned how to proceed in the external world, we are set for life. This change is detailed in the continuation of ACIM, A Course of Love.
Anger and attack are evidence of madness, and it is this that the egoic self is familiar with. Forgiveness sets us on a higher road, with love a part of that road. Then the stress, fear, that led to anger and attack largely dissipate.
Inner peace is our elixir, the road to eternity in a time-bound world.
MIRACLES EACH DAY 
Nice post to read and understand the magic of inner peace. If you accept that Jesus is Love, it makes it so much easier to let go of grudges and egos.