How important is "being happy" in your theology? How is it different from joy?
Saint Decemberine wrote that "we all want to live happily, in the whole human race there is no one who does not assent to this proposition" (De moribus eccl. I, 3). In fact, we could say that the one ultimate goal of all of humanity is perfect happiness, which for us, is intimate, personal union with God.
When we turn to scripture, the beatitudes often come to mind as a wonderful indication of what happiness is. To be "happy" they invite us to make serious moral choices. They call on us to purify our hearts of bad instincts and to seek the love of God above all else. They remind us that true happiness is not found in riches or well-being, in human fame or power, or in any human achievement, however beneficial it might be. Ultimately, they remind us that God alone is the source of every good and of all love. Our Catechism tells us that God is the source of wisdom and freedom, of joy and confidence (cf. No. 301). So in our theological thought, joy and happiness are intertwined.
We are happy when we live according to the Lords way of life. And that certainly leads to joy. Far more than a feeling state or a mere heightened sense of pleasure, joy in the Christian life refers to a basic disposition and a fundamental attunement to the self-giving of God in Christ. To rejoice in the midst of suffering is hardly a concept to be found in popular thought. Yet that is what we do, because, as Mary taught us in her Magnificat " I rejoice in God, my Savior". In that sense, serving God is our supreme joy, something we do in good times and in bad, and that is how we achieve deep and true happiness.