Allah says in Sura Al Araf V:201: Verily, those who are pious (or God fearing), when an evil thought comes to them from Satan, they remember (Allah) and indeed they then see.
It is known that evil whisperings in one’s heart and bad thoughts can take root in one’s mind and change into willingness and this may change into determinations which can subsequently manifest as action and when done repeatedly becomes a habit. So if these whisperings are blocked at the beginning then one will get rid of the above chain of events thus saving one from all it consequences. But if you accept these whisperings and allow it to develop further then it will eventually lead you to evil action and even if it fails to result in any action it can still create an evil desire in your heart.
It is clear that preventing such evil whispering taking root in the first instance is easier than blocking out established thoughts and preventing the latter is easier than stopping one’s intention and determination to carry out a bad deed and preventing a bad deed is easier than getting rid of a bad habit. Hence priority should be given to prevent the initial steps i.e. evil whispering, bad thoughts and determination.
One’s attitude towards these whispering does determine one’s true character and could either bring you closer or lead you away from your God whom you worship seeking His Mercy. As true happiness and success in life cannot be achieved unless you get closer to Him and gain His pleasure by being obedient to Him and following His instructions. Otherwise by being away from Him one will face hardship and gain the displeasure of Allah .
One of the Mercies which Allah grants to believers is that He will not hold a believer accountable for evil whispering unless it leads to a bad deed. According to Abu Huraiyra (RAA) that the Prophet (PBUH) said: Verily Allah will not hold my Umma accountable for evil whispering in their hearts unless it manifests into talk or action.