The Psalmist commands us to “make a noise, serve the Lord, enter His presence and give thanks” for two reasons: first, because we are His (v3) and secondly because He is good (v5). These two reasons together motivate us to worship. If we are not His, what He is like doesn’t matter. If we are His, but he isn’t good, it is terrifying.
True Worship is a “joyful noise” and “glad service” (v1, 2). We express our gratitude and thanksgiving (v4) to our God by words of praise and acts of obedience. A God who is both powerful and good is worthy of our full worship.