Turn away from evil and do good; seek peace and pursue it.   (Ps. 33:14)

And the peace of God, which passeth all understanding, shall keep your heart and minds through Christ Jesus. (Phil. 4:7) 

Surely [peacel is nothing else but a loving disposition towards one’s neighbor. Now what is held to be the opposite of love? It is hate and wrath, anger and envy, harboring resentment as well as hypocrisy and the calamity of war. Do you see for how many different diseases this single word is an antidote? For peace is equally opposed to every one of the things mentioned, and wipes out these evils by its own presence. Just as illness vanishes when health supervenes, and as no darkness is left when light begins to shine, so also when peace appears, all the passions connected with its opposite are eliminated –St. Gregory of Nyssa 

How much joy, how much peace of soul would a man not have wherever he went…if he was one who habitually accused himself. –Abba Dorotheos 

Peace is the integrity and health of the soul; to lose peace is to lose spiritual health…. When my soul is filled with a holy peace, then surely the King of Peace–the Lord Jesus Christ–dwells within me.  –St. John of Kronstadt