When we greet one another at church we say: “Peace be with you” which was a greeting used in the New Testament among Jesus’ Apostles. Jesus told them: “My peace I give you” which is the peace of mind in knowing you’re a child of God which comes with a variety of beautiful aspects such as: 1) Knowing we’re just passing through and that all things both good and bad will pass, we just have to hang in there and ride it out. 2) Knowing that all things are possible thus giving us hope. It doesn’t mean that what we desire will definitely happen, but knowing it could, can be very comforting during critical times. 3) Knowing that trying to do good matters to God even if we don’t see the outcome or if it is sometimes unappreciated. 4) Believing we’ll see our loved ones someday. Even if we’re spiritual beings when we get to heaven lacking a human form, most Christians believe we'll know each other. We’ll be different because we won’t have the same mental and physical baggage we carried as human beings so our love will be even stronger than we can ever imagine.
All of the above things bring a tremendous amount of peace to Christians. We could be wrong about believing the things we do which we won’t know for sure until we die but the comfort and peace we get from believing here and now, help make our lives so much more joyful. I guarantee you in most cases more joyful than most atheists or agnostics.