Psalm 95 has no title in the Hebrew, though in the New Testament Hebrews 4:7 says God spoke these words through David. It is a call to worship with two invitations and a warning. The first invitation is loud: Oh come, let's sing to Yahweh. Let's shout aloud to the rock of our salvation! The reason is God's kingship over creation: in his hand are the deep places of the earth and the heights of the mountains. The sea is his, and he made it.
The second invitation moves from shouting to kneeling. Oh come, let's worship and bow down. Let's kneel before Yahweh, our Maker. Now God is not only the Maker of the world but the Shepherd of his people: We are the people of his pasture, and the sheep in his care. Praise for God's greatness leads to humble surrender.
The warning turns from singing to listening. Today, oh that you would hear his voice! Don't harden your heart, as at Meribah, as in the day of Massah in the wilderness. That generation saw God's works yet tested him, and God said they would not enter his rest. Hebrews 3 and 4 apply this to Christians: Today is the time to listen, and God's rest is still offered to those who believe.