Happiness is a result of our current circumstances. We are happy when something is going on around us that makes us happy. On the other hand, Peace is an attitude. Our attitude is a choice we make. We can choose to be happy when something bad is happening in our life but that happiness is typically contrived or fake. We can choose to have the right attitude. An attitude of gratefulness. An attitude of contentment. An attitude of peace. Those attitudes are typically hard to adopt when our circumstances are difficult but God doesn't expect us to adopt those attitudes by our own strength.
Lord, help me to have an attitude of Christ and not simply have feelings based on my circumstances.