Imam Khomeini explains the matter in his famous work of "Forty Hadith" as following:
You will also notice that obedience to God gives ample pleasure. Though this world is not where one is immediately rewarded, yet faithfulness to God and abstaining from sins is fruitful in this world also.
God never entrusts His creatures with cumbersome and heavy tasks, which are beyond their powers, but it is the Satan and his allies who magnify them in your view.
God forbid, if there are any lapses on your part, ask God’s forgiveness, and beseechingly implore Him that you will be more careful in future, so that the Almighty may throw open the doors of His grace and compassion to you, and may guide you in the straight path.