For those that believe, God's purpose for us is to worship him...

For those that believe, God's purpose for us is to worship him and he tests which of us are good in this, he can reward/punish in this life or the next.
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“So how do you know the mind of God?”
We don’t, we can only go by his words in the Qur’an and the teachings of Muhammad in his explanations

Why is God a He?
Yes may be an It (light) or She, but most often refereed to as He – He likes to maintain the mystery you know, like the mysterious letters (Muqatta’at) at the beginning of 29 out of the 114 surahs (a combination of between one and five Arabic letters) – the meaning of which are only known to God, saying he not let us have all the knowledge.

How do you know God can reward or punish us?
You seen the after effects from Sodom and Gomorrah, and various other acts of God as described in the Scriptures, parting of the Red Seas, etc

How do you know there is an afterlife?
This one we don’t know, but its our belief same as Christians, we all die, resurrected and Judged, some here say we self judge and heaven and hell is in our minds – I’m open minded about the unseen – but the Qur’an describes what is in Heaven and how Hell will be like – virtual or real – we’ll all know one day

All you say is belief and not truth. The only way to know what you say is to know absolute truth and you will probably be the first to achieve that.
Yes but we believe enough is truth to try to change our characters to a more moral and virtuous life rather than following our own vices or ones marketed to us.

As a gambling man IMO the odds of you being in possession of absolute truth is near enough to zero.
Agree we don’t have all the knowledge