Every day is joyful because…
It is the day the Lord has made. We are to rejoice and be glad in it (Ps 118:24),
God is glorifying His name constantly (Jn 12:28),
God is conforming every one of His children to image of Jesus (Ro 8:29),
God is laying up treasures in heaven for all His children (2 Tim 4:8),
God has everything (!) under control (Is 46:9-10; Eph 1:11),
God gives you whatever AND everything you will need for whatever you encounter (2 Cor 3:5, 2 Pet 1:3-4),
Jesus may return today (Mk 13:33).
With just THOSE things being true, how can there not be joy in THIS day and every day?!