Maulana Ashraf Ali Thanvi rehmatullah alayh says,
“One letter came which said that, “I have been thinking a lot about which sin I might have committed in lieu of which I am facing such difficulties.” I replied to him that the time when you did not have any difficulty, did you ever think in lieu of which good deeds are you relishing the good easy life?
“He kept thinking all of his good deeds to be accepted and a collective cause in his comfortable life. At that time he did not pay attention as to which particular good deed would cause this life. But when difficulty arose, he started differentiating between the sins. Which sin is causing this difficulty or calamity?
“(The truth is that) People do not think Sagheera (minor) sins to be of any value. Whereas they are minor only because of the comparison to the major sins, but by themselves there is nothing minor about them. An example of this is that of ember (a spark). There is nothing small or a big about it, even a small ember is enough to burn the whole house to the ground.”
Malfuzaat Hakeemul Ummat Malfuz # 352 – vol. 1 pg. 264