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.John 14:27 (KJV)
John 14 is one of the most profound books of the Bible. In it, we hear Jesus talking to His disciples about things that are to come, the rise of the Holy Spirit into their hearts, and the understanding that the Father is in the Son. Twice in this chapter He instructs the disciples to let their hearts not be troubled. He is leaving the earth in His current form and they are to understand that this is a good thing. He is comforting them and reminding them of the joy that His resurrection shall bring to the lost souls of the world.