If the almighty God is the greatest, why does he wants us to pray? To make him happy?
I don’t think so.
When you offer prayers, you think of God. When you do it regularly, in Islam is five times a day, you are at least five times with God. The more you occupy yourself with God, the more you will pause and think before acting.
You will also improve your conscience. Your conscience will tell you if you’re in the wrong path. You will feel it. You know it before your brain interrupts. When you follow that you will be in the right path most of the time. Your choices will be better, and you will grow gradually by the accumulation of that small good choices.
We pray not to make God happy but to save ourselves to live the right way.
“I can be good with or without God, why need him?”
You’re smart. But you need more than smart. You can’t only rely on your brain. It can get exhausted and you will make mistakes.
You also need a perfect soul. A good heart will lead a good brain.
When you are close to God. You will meet him in everything you do. You know he is the kindest, the most merciful, the most beneficent, and the most forgiving.
You will strive towards that and live on the right path.