Did you know that God commands us to be glad?
"Delight yourself in the Lord and he will give you the desires of your heart." (Psalm 37:4)
1) God created us for his glory
"Bring my sons from afar and my daughters from the ends of the earth,... whom I created for my glory" (Isaiah 43:6-7)
God made us to magnify his greatness - the way telescopes magnify stars. He created us to put his goodness and truth and beauty and wisdom and justice on display. The greatest display of God's glory comes from deep delight in all that he is. This means that God gets the praise and we get the pleasure. God created us so that he is most glorified in us when we are most satisfied in him.
2) Every human should live for God's glory
"So whether you eat or drink or whatever you do, do it all for the glory of God" (1 Corinthians 10:31).
If God made us for his glory, it is clear that we should live for his glory. Our duty comes from his design. So our first obligation is to show God's value by being satisfied with all that he is for us. This is the essence of loving God (Matthew 22:37) and trusting him (1 John 5:3-4) and being thankful to him (Psalm 100:2-4) It is the root of all true obedience, especially loving others (Colossians 1:4-5).
3) All of us have failed to glorify God as we should
"All have sinned and fall short of the glory of God" (Romans 3:23).
What does it mean to "fall short of the glory of God?" It means that none of us has trusted and treasured God the way we should. We have not been satisfied with his greatness and walked in his ways. We have sought our satisfaction in other things, and treated them as more valuable than God, which is the essence of idolatry (Romans 1:21-23). Since sin came into the world we have all been deeply resistant to having God as our all-satisfying treasure (Ephesians 2:3). This is an appalling offense to the greatness of God (Jeremiah 2:12-13).
Read more: Find True Joy in Jesus