Greetings in that Divine and Most Precious Name of Our Lord and Savior Jesus Christ!
My own two cents:
Human emotions come realistically in two, and only two varieties: fear and love. Anger and sadness stem from fear. When folks are angry, they are really just expressing their fear at a lack of control of a given situation or circumstance which has angered them. When folks are sad or grieving, it is the same fear manifested in a different way, but fear all the same, as folks are afraid of the lack of control and the pain it causes. Love on the other hand, builds joy, peace, and harmony. When we are growing in love, we grow with God. When we are falling into fear, we are pushing ourselves away from God like Adam and Eve did when they were afraid in the Garden of Eden. Like the Apostle Paul tells us, "Perfect love casts out all fear."
So we realistically shouldn't let ourselves get angry, even if in the sense of righteous indignation, because the reality is that anger is fear, and with God in our lives, what do we really need to be afraid of? Why should we be overwhelmed by anger when God is at the helm? Why should we let sadness blacken our lives when God is always near? We need to cultivate and build love, and fear will only challenge our ability to love the others, to love God, and to love own self.
Father Meletios talks about this as well, when he mentions that we can't rely upon our emotions, because they stem from our broken personalities, the gap between heart and mind. Emotions he argues, come from the fractured mind, they are shallow and unreliable. Faith in God comes from the heart, which is Love. We then need by fasting and prayer to learn how to not get caught up in our emotions, which are really just fear or love, and instead, follow our hearts to God.