Peace is available to Christians. It's one of the fruits of the spirit. But the definition or look of peace sometimes is more of a question when our hearts seem restless or anxious and when it's simply only used as a way to say goodbye: "Peace, man."
In the Bible, Paul often used it in greetings. There's a great importance to something if it appears so often in the Bible.
Beyond the Holy Spirit's work in our lives (where we know it's not us but God working in us), how does a person get to this feeling or state of peace? First, so we're not too hard on ourselves or too anxious to get to a state of peace faster than is possible, we need to acknowledge that we're in a fallen world, where true perfection is not gained here but in Heaven, and we're also growing over time. We should aim to grow, because we love God, and we know this relates to him in some way.
Often Paul uses the term "peace" right next to "grace." The more often we think of the grace of God, in sending his son for us, the more often we feel at peace. Grace means we don't have to do anything to gain favor. We've been granted freedom. Freedom from death and sin. We are still sinners, but we're saved. And we're a part of God's family. We're not alone.
Another way to feel at peace is to study God's word and nature enough to know what God wants of his people. We know what our purpose is here on—which is to love God and enjoy him, and to also love others. We feel at peace when we know we're doing what our good Father wants us to do and he knows we're most happy when we do—loving him and being generous and loving to others. When we do things that are generous and loving, we see and feel some beauty in it.Of course it needs to be done in a wise way, where we don't cause unnecessary harm to ourselves in the process. An example is giving so much you run out of money yourself or being so tired you aren't a help anymore but need help.
Giving to and loving others helps us feel less alone and more connected. That can bring peace too.