We praise God alone and with one another to glorify Him and be in His presence. We praise Him also because God is coming back again.
This idea of God coming back again is more than us living forever in heaven. When God comes back, absolute justice will land on earth.
There is many many crimes and injustices done on the earth that have never been solved. Sin and rebellion has crippled humanity and many have suffered and perished unjustified. God judges with equity. There is no bribes we can pay to him to satisfy his righteousness. There is no favour we can do to escape His holiness. The only one who can present us before God pure and justified is Jesus Christ. We see the Father dressed in His robe of righteousness. Only that way we can see the New Heaven and earth and enjoy the world put right by the magnificent King.