Christians are motivated by joy and the treasure that is ours in Christ (Mt 13:44). Our treasure is Christ himself – knowing Christ and being righteous in him. This joy leads to a willingness to suffer for Christ (Philippians 3:7-11). Our treasure is also eternal glory = being with Christ forever (Philippians 3:20-21). Other Christians are also our joy (Philippians 4:1). Because we treasure Christ, it is a joy for us to see other people worship him and to see Christ formed in them.
Joy is commanded of Christians (4:4). Joy is an antidote to disunity because I delight in Christ rather than being preoccupied with myself and how others treat me (4:2-3). Joy is an antidote to worry because what I treasure is Christ and my possession of him is secure (4:6-7). Joy in Christ creates contentment whatever the circumstances of my life (4:10-13). Loss becomes an opportunity to treasure in Christ.