Joy is a state of grace that is given by God even in the midst of horrible grief and sorrow. Joy is rooted in the love and grace that Jesus showed us is in the heart of God. And the mark of a healthy church is the joy of its members. You can walk into a church and know whether or not there is joy. You can sense it.
Christians are thankful people.
We are grateful because we have received God's grace in Christ. Our lives are marked by a deep gratitude and heartfelt thankfulness to God, even for the simplest, the most ordinary things in life. When I traveled in Kenya my days were filled with spontaneous prayer, with constant reminders that here and there God's presence was in our midst, calling forth a response. The Kenyan Presbyterians would pray before they got into a car and asked for a safe journey and we prayed thanking God for the gasoline that brought us to where we need to go to do God's work. We recalled to mind all that we experienced in a day and we gave thanks for it.