Since the beginning, religion has taught mankind that the Lord is angry with our behaviour and He must be appeased - that we must do something or stop doing something in order to have peace with Him.
At the heart of this concept is a basic Truth - the spirit of rebellion and the resultant sin separated man from the Lord.
But the idea that good behaviour is what the Lord wanted from man was all wrong. The Lord wanted an intimate, personal relationship with each of us.
In order for sinful man to be in relationship with his holy Creator, the Lord Himself had to pay the penalty for sin. And to fix the sin of rebellion, He had to give us a New Spirit - a part of Himself.
So, it is in the amazing Grace of the Lord that peace is established eliminating worries, fears, and doubt while stabilizing our minds and hearts through the perfect work of Christ Jesus.
The peace passes our understanding because the love of the Lord is immeasurable.
The above is regarding Internal Peace which comes from being Born Again as Sons Of The Holy Spirit by Grace Through Faith into an intimate personal relationship with the Lord Jesus Christ.