Rejoicing in the LORD

Was Paul going through a great time of blessing in his own life at the time he wrote these verses? How can one rejoice when in deep trials? What does it mean to rejoice? Is the LORD sovereign? What causes us the most trouble in this world? What does LORD mean? What is the Gospel? How do we see Christ cleansing blood in the Gospel as the only hope? Where is Christ now? How has He put our names in His Book of Life? When were our names put in the Lamb's Book of Life? Can anything happen to us that does not come from His hand? Why does the LORD bring us through trials? Does God answer every prayer of His children?