Why does God exist?

I am a 15-year-old student doing Religious Education studies at school. In a recent lesson we had a debate about Thomas Aquinas' theory that there is a reason for everything. We got to a stage where a majority of the students whom are atheist questioned us theists that if there is a reason for everything then what was the reason for the existence of God (Allah, swt). If you could please shed some light on this question I will be very grateful.

Walaikum assalam wa rahmatullah,

God simply must exist. It is as simple as that.

The nature of the existence of God is different from the existence of creation:

God’s existence is necessary and entailed in of itself. He can not ‘not be.’

The existence of created things is contingent, and only possible through God's acts of creating and sustaining.

Note that, Islamically, the ‘reason’ for the creation of anything is because God chose to create it. It is not necessary for God to create or not create anything, for God is not conditioned by any of our human suppositions or categorizations.

And Allah alone gives success.

Wassalam,

Faraz Rabbani