[2:21-22] Why worship God?

[2:21] O Humans
worship your Lord
who created you
and those before you
so that you have caution.
[2:22] who made for you the Earth a spread [like a bed]
and the sky a cover [like a canopy]
and sent down from the sky water
so [that] it brought out some fruits
a provision for you
so don't make equals to god while you know


The above verses explain some of the many reasons why humans should worship God and become the "Cautious" instead of the "Rejecters" or Hypocrites. 

1. He created you and all humans who have ever existed (and by extension - all those who will ever exist)

The next few reasons are cleverly phrased to show how they interrelate.  So that God shows He not only gives us sustenance, provisions and protection but He has made everything in such a way that it is connected, cyclic or interrelated in a life-sustaining system.

• The earth (we are land based creatures - i.e. a water or gas world would see us quickly killed off)

• The sky a cover (our atmosphere is crucial for allowing life on Earth - protecting it from harmful cosmic rays and asteroids. It also allows a steady temperature to be maintained - without an atmosphere days would be scorching hot and nights freezing cold - without an atmosphere the planet would become a "dead" rock - much like the moon (that has no atmosphere / sky).

• Rain (life on earth depends on water.  Rain allows water to be distributed across the land.)

• Fruits (from the water, plant life grows and contributes to human and animal sustenance as part of the food chain.  Without fruits humans would quickly die.  Without rain, there'd be no fruits, and humans would quickly die.  Thus God shows us how fragile and weak we are - how dependent we are upon Him and the system He made (of which we are a part)).

So in exchange for all these things God has made- we are only asked to accept the truth - that our Creator is One (and thus not make anything else equal with Him) and worship Him alone.