Why do Christians rejoice in God's reign?

The psalmist encourages the earth to rejoice at God's reign because it signifies His sovereign goodness and the blessings of His kingdom. For Christians, this reign means that they are part of a new spiritual reality established by grace. Joyful confidence in God's governance fosters a deep-seated assurance amidst trials and tribulations, knowing that He ultimately works everything for their good. The assurance of eternal life and the hope of salvation also fuel this rejoicing, as they anticipate a full realization of His kingdom in glory.