Imam Gazzali (R) writes: If shunning the sins and preparing for worship are the key-points of submission, those can never be attained without fear and hope. A disobedient animal has to be pulled forward and hit from the back. If it lies down somewhere, on one hand the grass is shown and on the other hand it is battered. Only then it would move forward.
Similarly, the unruly children cannot advance in their study without their fathers temptation and teachers scolding. Human beings are also disobedient by nature. On one hand it’s nafs (the lower self) has to be admonished by the fear of Jahannam and on the other hand it needs to be enticed through instilling the hope of Jannah. Therefore, one who desires to strive on the path of worship, should manage and control the ‘nafs’ (his nature) through this way, i.e. impose the fear of Jahannam and attract it toward Jannah. Otherwise, the disobedient nature would never submit and come under control. The Holy Quran has mentioned both these two points several times. There are descriptions of reward to such an extent that to refrain from their appeal is difficult. And there are descriptions of punishment to such an extent that getting frightened of those are obvious. Therefore, to reach the goal of worship, regularly discuss these two points. This would alleviate your pains and hardship.
Translated from Minhajul Abedeen of Imam Gazzali (R)