Joy

⁹ Therefore my heart is glad and my tongue rejoices;
    my body also will rest secure,

Your heart can be glad because you know the secret to joy. True joy is far deeper than happiness. You can feel joy in spite of your deepest troubles. Happiness is temporary. Joy is lasting. Do not base your life on circumstances. Base your life on God.  As you understand your relationship and future with God, you will experience true joy.