What is the reason of serving ?
We know that every mankind has two aspects
1- physical needing
2- moral needing
So as every person deeds to physical meal he needs to moral meal
When we sea quran we find a lot of verses explain the reason of serving gog
1- because god is needless absolutely as he is our creator so we need to
him absolutely
يَا أَيُّهَا النَّاسُ أَنتُمُ الْفُقَرَاء إِلَى اللَّهِ وَاللَّهُ هُوَ الْغَنِيُّ الْحَمِيدُ- verse 15. chapter fater
o men! you are they who stand in need of allah, and allah is he who is the self-sufficient, the praised one

2-every person need to perfection and it is not possible except serving god
الذين جاهدوا فينا لنهدينهم سبلنا.. chapter ancabot – verse 2
and (as for) those who strive hard for us, we will most certainly guide them in our ways; and allah is most surely with the doers of good
3- every person likes get benefit
وَمَن جَاهَدَ فَإِنَّمَا يُجَاهِدُ لِنَفْسِهِ إِنَّ اللَّهَ لَغَنِيٌّ عَنِ الْعَالَمِينَ. chapter ancabot – verse 6
and whoever strives hard, he strives only for his own soul; most surely allah is self-sufficient, above (need of) the worlds

4- serving god avoids human from indecency and evil
إِنَّ الصَّلَاةَ تَنْهَى عَنِ الْفَحْشَاء وَالْمُنكَرِ....chapter ancabot – verse 45
surely prayer keeps (one) away from indecency and evil

5- finally serving god avoids person from every injustice
وَلَقَدْ بَعَثْنَا فِي كُلِّ أُمَّةٍ رَّسُولاً أَنِ اعْبُدُواْ اللّهَ وَاجْتَنِبُواْ الطَّاغُوتَ.. chapter nahl – verse 36
and certainly we raised in every nation a messenger saying: serve allah and shun the shaitan