All are called to sing and make music in praise of the Lord–including even the seas, floods, and hills.
This is one of a group of songs that announce and praise the kingly rule of God. Many contain the sentence “The Lord is king” or something quite like it (Psalms 93; 95; 96; 97; 99), which has caused many scholars to think they were sung at a festival (perhaps in The fall refers specifically to the disobedience of Adam and Eve when they listened to Satan rather than adhering to God's command not to eat the fruit from the tree. When people act contrary to God's will, they are said to fall from from grace...) announcing anew God’s enthronement and celebrating God’s rule. Whether or not that is true, this group of psalms does give praise to God as the ruler and A righteous person is one who is ethical and faithful to God's covenant. Righteousness in the Old Testament is an attitude of God; in the New Testament it is a gift of God through grace. In the New Testament righteousness is a relationship with God... judge of all the earth.
God’s rule deserves to be celebrated, precisely because God alone judges with complete righteousness and equity (v. 9). So, everyone and everything sings praises, plays lyres, trumpets, and horns, and makes a joyful noise before the Lord (vv. 4-6). Even the sea roars, the floods clap their hands, and the hills sing for joy. Under righteous rule, everything prospers (people and all creatures), so everything joins in praise.