Imam Khomeini explains the matter through his famous book "Combat with the Self" as following:
How long do you wish to remain in the sleep of negligence, plunged in corruption? Fear God! Beware of the aftermath of your deeds! Wake up from the sleep of negligence! You have not yet awakened.
You have not yet taken the first step. The first step of wayfaring is yaqzah (awakening), but you are still asleep.
Your eyes may be open, but your hearts are asleep.
If your hearts were not so sleepy and rusted and blackened with the effects of sin, you would not continue your wrongful deeds and words so carelessly and indifferently.
If you thought a bit about the affairs of the other world and its terrible path you would give more importance to the heavy duties and responsibilities which rest upon your shoulders, Imam further explained.
There is also another world for you, there is also the resurrection. (You are not like other existents for which there is no returning.) Why do you not take warning? Why are you not awake and conscious? Why do you so heedlessly engage in backbiting and speaking ill of your Muslim brothers, or listening to such things? Do you not know that the tongue which wags in backbiting will be trampled under the feet of others on the day of resurrection?
Have you heard that backbiting will be food for the dogs of hell? Have you never given a thought to how evil are the consequences of these differences, enmities, jealousies, cynicism and selfishness, and arrogance and conceit? Do you know that repercussion of these wicked forbidden deeds is hell and that it is possible, God forbid, that they will lead to the everlasting fire?
Read more:
The great prophets of God were sent to this world with the light of Divine Laws