The unsaved can never have real peace because of the conviction of the HOLY SPIRIT. Believers have peace when they are living a life dedicated to the Lord, by not getting caught-up in the ways of the world. When believers stop walking in the SPIRIT (Galatians 5.16) and stop being led by the SPIRIT (Galatians 5.18) they have no peace.
Peace only comes by faithfully living a life of true surrender and devotion to Christ, which includes daily prayer, Bible reading, study, memorization and meditation, along with regular fellowship with the brethren, sharing the gospel with the lost and making disciples. The more we give to others the more peace we will have. Living a self-centered competitive lifestyle is a sure way to make oneself miserable and be out of the will of God. By staying in close communion with the Lord His peace will take over our lives.
“Peace I leave with you, My peace I give to you; not as the world gives do I give to you. Let not your heart be troubled, neither let it be afraid” (John 14:27).