Tell me what pleases you and I will tell who you are. What makes a believer pleased is his obedience to Allah,

Dr. Umar Abdul Kafi:

He is pleased because of Islam in the first place.

Dr. Nabulsi: 

If the reason of your pleasure is money, your happiness is temporary, because this money would leave you.

Because this money would leave you. Allah the Almighty has not allowed the worldly life to provide man with a growing or continuing happiness, but rather a decreasing one. Moreover, due to Profound Wisdom and to His love to us, Allah the almighty has made the worldly life unsatisfying, because man's soul is eternal. Man has chosen to believe in Allah the Almighty in Alam Al-azal (the World of souls), and this choice requires having an eternal soul. Therefore, when he chooses to be satisfied with temporary things he falls.