The ability to speak and communicate with others is one of the greatest blessings that Allah has bestowed upon the man. We can make friends or enemies by mere use of our tongues for it is the words that we speak can please or hurt someone. It is said that the bullet shot from a gun and the words once spoken can never be taken back. Therefore the need to select words very appropriately before their utterance. Remember whatever we speak can have an everlasting effect on the audience and any negativity expressed when in bad mood or anger can induce depression on the listener and hurt him far beyond our expectations.
It is said that you can say something hurtful in ten seconds, yet even after ten years the wounds will be found unhealed and fresh. So one can be very careful of what one speaks. For once something is said, it may be forgiven, but NEVER FORGOTTEN.
And there is more to it other than hurting others. Whatever we say or whatever actions we take these are recorded by two angels posted on each person's shoulder who record each of our actions, gestures and words, unknown to us, and the same will be presented on the Day of Resurrection in the form a dossier which will finally make up our case of reward or punishment.
This is exactly what is being said in the 18th verse of Surah 50. Qaf of the Qur'an:
مَا يَلۡفِظُ مِنۡ قَوۡلٍ اِلَّا لَدَيۡهِ رَقِيۡبٌ عَتِيۡدٌ
(50:18) He utters not a word, but there is a vigilant watcher at hand.
That is, "On the one hand, We Our self directly know man's actions and movements, even his hidden thoughts; on the other, every man has two angels appointed over him, who are recording whatever he does and says; none of his actions or words is left unrecorded. " This means that when man is produced in the Court of Allah, Allah at that time Himself also will be knowing what each person has done in the world; besides, there will also be two witnesses who will produce documentary evidence of the person's actions and deeds. As to what will be the nature of this documentary evidence, it is difficult for us to have a precise conception of it. But from the facts that we are witnessing today, it seems certain that the voices and pictures and marks of man's actions and movements are being preserved and imprinted on every particle of the environment in which he lives and works, and each one of these can be reproduced in exactly the same form and voice so as to Leave no difference whatever between the original and its copy. Man is doing this on a very limited scale with the help of his inventions, but the angels of God neither stand in need of these machines nor are bound by any limitation. Man's own body and everything around it is their tape and their film upon which they can record every voice and every image along with its minutest and most delicate detail precisely and exactly, and can make man hear, on the Day of Resurrection, with his own ears, in his own voice, those very things which he talked in the world, and can make him see, with his own eyes, the pictures of all his misdeeds, whose genuineness he would not possibly be able to deny.
Here, one should also understand that in the Court of the Hereafter Allah will not punish anybody only on the basis of His own knowledge, but will punish him after fulfilling all the requirements of justice. That is why an exhaustive record is being got prepared of every person's words and deeds in the world so that a complete proof with undeniable evidence becomes available of everyone's life-work and activity.
Tafsir Ibn-Kathir:
That is (whatever he utters), in reference to the human, (of a word), means any word that he or she speaks, (but there is a watcher by him ready.) means, but there is a scribe whose job is to record it, leaving no word or movement unrecorded.
Allah the Exalted said, (But verily, over you (are appointed angels) to watch you, Kiraman (honorable) Katibin writing down (your deeds), they know all that you do.) (82:10-12)
Therefore, the scribe records every word that is spoken, according to the explanation of Al-Hasan and Qatadah. This is also the apparent meaning of this Ayah.
Imam Ahmad recorded that Bilal bin Al-Harith Al-Muzani said, "The Messenger of Allah said:
(Verily, a man might utter a word that pleases Allah the Exalted, unaware of how highly it will be regarded, and on its account Allah the Exalted and Most Honored decrees His pleasure of him until the Day he meets Him. A man might indeed utter a word that angers Allah the Exalted, unaware of how dreadful it will be and on its account Allah the Exalted decrees for him His anger until the Day he meets Him.)'' `
Alqamah used to say, "How many words did I not utter because of the Hadith that Bilal bin Al-Harith narrated.'' At-Tirmidhi, An-Nasa'i and Ibn Majah collected this Hadith. At-Tirmidhi said, "Hasan Sahih.'' There is a Hadith similar to this in the Sahih.
Yusuf Ali Explanation:
Then each "word" spoken is taken down by a guardian (raqib). This has been construed to mean that the guardian only records words, not thoughts which are not uttered. Thoughts may be forgiven if not uttered, and still more if they do not issue in action. At the stage at which we clothe a thought in words, we have already done an action. The Recorders mentioned in the last verse make a complete Record, in order to supply motives and springs of action, which will affect the degrees or status in the Hereafter. The three together, individuals or kinds, make the honourable Recorders, Kiraman Katibin, (plural, not dual number) mentioned in lxxii. 11.
Qur'an Wiki:
It is enough that we should appreciate this fact, expressed here in a vivid picture, and feel when we are about to make any movement or utter a word that, to our right and left, there are two watch-guards taking note of whatever we do or say, entering it in our record which will be presented to God who overlooks nothing. This is a fact, even though we may not understand how it is done. There is no doubt that it takes place, in some form. God has told us about it so that we take it into account, but also so we do not waste time and effort in trying to determine how it is done.
Javed Ahmad Ghamidi Explanation:
For conclusive communication of the truth, a further arrangement made by God is that He has deputed two angels, one each to the right and left of each person so that they are able to prepare a record of his good and bad words and deeds for the court of God.