This verse is quite clear about what we need to do: Rejoice! The writer, Paul, even says so twice to get the point across.
Often it can be hard to find things to be joyful and happy about but, even if your life feels a mess, we, as Christians, will always have something to rejoice about. God has set us free from sin, has redeemed and forgiven us – we who deserve nothing! He loves us so much He gave up His Son for us.
No matter how dreary the day seems, let’s remember that we have plenty to be glad about – so rejoice in the Lord’s forgiveness and walk in the freedom which that joy can bring! 😀