Correct use of one's power of speech is an effective source of correcting all deeds issuing forth from other parts of the body
The basic command given to all Muslims in this verse is: اِتَّقُوا اللہَ (Take to taqwa, that is, fear Allah and act accordingly). The reality of taqwa lies in one's total obedience to all Divine injunctions whereby one carries out everything enjoined and abstains from everything declared prohibited and repugnant. And it is obvious that doing so is no easy task for human beings. Therefore, immediately after the main guideline of اتَّقُوا اللَّـهَ (ittaqullah: Fear Allah and act accordingly), there appears an instruction to start doing something particular, that is, the correction and reform of one's speech. Though, this too is nothing but a part of taqwa itself, yet it is one such part of it that, should this thing come under control, all other remaining components of the comprehensive requirement of taqwa would start becoming achievable automatically, as the verse itself has promised that, as a result of one's making his or her speech truthful and straight, Allah will correct his deeds. In other words it means that, 'should you succeed in holding your tongue and avoiding errors of speech and get used to saying what is correct, straight and right, Allah Ta’ ala will correct every other deed you do and make all of them better.' Then, concluding the verse, another promise was made and it was said: يُصْلِحْ لَكُمْ أَعْمَالَكُمْ (and He will forgive for you your sins). It means: 'One who gains control over his tongue, learns to harness his or her power of speech and becomes used to saying what is true and right, then, Allah Ta` a1a will take care of the rest of his or her deeds, have them corrected and made better as well as forgive any errors or slips made therein.'
Injunctions of the Qur'an were made easy to follow
Deliberation in the general style of the noble Qur'an shows that at a place where acting upon a Qura'nic injunction seems to be difficult, a method has also been suggested along with it to make it easy. And since taqwa is the essence of the entire religion of Islam and fulfilling its dictates on all counts is very hard indeed, therefore, speaking generally, wherever the command to observe taqwa ('ittaqullah' ) has been given, there appears soon after, the suggestion to do something that facilitates acting in accordance with the rest of the elements of Taqwa, something that comes from the side of Allah as His grace and taufiq. An apt and ready at hand example of it lies in this very verse where the suggestion of: قُولُوا قَوْلًا سَدِيدًا (say the right thing) follows soon after the command of: اتَّقُوا اللَّـهَ (ittaqullah: Fear Allah). And immediately earlier too, in verse 69, after saying: اتَّقُوا اللَّـهَ ittaqullah:( Fear Allah), it was said: "Do not be like those who caused pain to Musa) whereby people were reminded that causing pain to righteous and favoured servants of Allah is the most serious impediment in the achievement of taqwa and, once this impediment was removed, the way to taqwa will become easy.
Similarly in another verse the command to observe Taqwa has been supplemented by the direction of having the company of 'truthful persons' (9.118) which means that the easiest way to acquire the quality of taqwa is to remain in the company of righteous people. At another place the command of taqwa is followed by the direction of pondering on what one has sent ahead for the Hereafter, because it leads one to observe Taqwa (59.18).
Saying what is right leads to doing what is right both here and Hereinafter
Shah ` Abdul-Qadir of Delhi (رح) has translated this verse in a way that leads to the conclusion that the promise of correction and betterment of deeds made to those who get used to speaking in straight forward manner is not restricted to religious deeds alone. In fact, everything one does in this material world is also included therein. Anyone who gets used to saying the right thing - that is, never lies, speaks with deliberation without erring or wavering, does not deceive anyone and does not say what would hurt - shall find his spiritual deeds for his eternal life in the Hereafter, also come out right for him. As for the things he must do to live in this mortal world, these too will turn for the better. (The Urdu speaking readers should refer to the original translation of Shah Abdul Qadir to have a taste of its sweetness-editor)