In The Name of Allaah, The Most Merciful, The Bestower of Mercy.
Allaah [The Most High] said:
يَـٰٓأَيُّہَا ٱلَّذِينَ ءَامَنُواْ لَا تُقَدِّمُواْ بَيۡنَ يَدَىِ ٱللَّهِ وَرَسُولِهِ
O you who believe! Do not put (yourselves) forward before Allah and His Messenger. [49:1]
Meaning: Do not say [anything in the religion] until he [sallal-laahu alayhi-wasallam] speaks and do not do [anything in the religion] until he commands you. Some of the Salaf said: There is no [religious] deed-even if it is small-except that it raises two [questions]: Why and How? Meaning: Why am I doing it and in what manner will I perform it?
The first affair is related to the main reason, cause and motive behind the action: Is the deed performed because of the share [i.e. goods] of worldly life received by the performer and the personal desires related to this worldly life, such as love of praise from the people or fear of rebuke; or to secure the beloved things of this temporal worldly life; or to repel those temporal hated affairs of this worldly life; or is it for the purpose of actualising servitude to Allaah, seeking after His love and a means of getting close to Him? The objective behind this question is: Is it obligated on you to perform this deed for the Sake of your Protected [or Guardian (Allaah)], or do you perform it in order to receive your share of this worldly life, or out of a mere desire of yours? The second affair is related to your adherence to the path of the Messenger in that act of worship– meaning: Is that deed something legislated by Allaah through the [authentic] Sunnah of His Messenger or is it a deed which Allaah has neither legislated nor is He pleased with it?
Therefore, the first affair is a question about sincerity and the second affair is a question about adherence to the path of the Messenger. The heart cannot be completely sound until it is safe from five affairs: Safe from Shirk which is the opposite of Tawheed; Safe from bidah which is the opposite of Sunnah; Safe from lusts which is the opposite of obedience; Safe from heedlessness which is opposite of being in a state of remembrance of Allaah, and safe from desires which is the opposite of adherence to the Sunnah and Sincerity.
Imaam Ibnul Qayyim [rahimahullaah] also said: Glorified be Allaah! How many a heart is decayed yet its owner is unaware of it! How many [a person] is put to trial by the praises he [receives] from the people, deceived by Allaah’s concealment of his [sins, shortcomings etc] and being gradually led to destruction through the blessings Allaah bestowed upon him [i.e. he utilizes those blessings to commit sins and feels safe from punishment]. All these affairs are a punishment and humiliation, whilst the ignorant one thinks that it is nobility. 
: [Source: An Excerpt from بدائع التفسير الجامع لما فسَّره الإمام ابن القيم الجوزية slightly paraphrased. Vol 2. Page: 276-277]; : [Al-Jawaab Al-Kaafi: page 140]