John 14:27 Peace I leave with you, my peace I give unto you: not as the world giveth, give I unto you. Let not your heart be troubled, neither let it be afraid.
Remember from John 10:10 that Satan is a thief and this gift given to us by Christ is a precious thing that Satan wants to steal from us. He attacks our peace with worldly cares and concerns.
Matthew 10:35-37 For I am come to set a man at variance against his father, and the daughter against her mother, and the daughter in law against her mother in law. And a man’s foes shall be they of his own household. He that loveth father or mother more than me is not worthy of me: and he that loveth son or daughter more than me is not worthy of me.
The enemy will attack your peace with God using your strongest allegiances and those may well be those of your own household. When I turned to Christ my own brothers turned against me. Painful as that was I had to choose Christ over family when family could not accept the new me.
I cannot imagine what my life would have been like if I had denied Christ for the sake of my sinful brothers. I did not and His peace remained with me. As hurtful as it was, the peace of God ensured my joy remained intact and the love continued to work in my life.
Romans 9:1 I say the truth in Christ, I lie not, my conscience also bearing me witness in the Holy Ghost,
1 Timothy 1:5 Now the end of the commandment is charity out of a pure heart, and of a good conscience, and of faith unfeigned:
Hebrews 10:22 Let us draw near with a true heart in full assurance of faith, having our hearts sprinkled from an evil conscience, and our bodies washed with pure water.
The new hearts barometer for peace is our new conscience.