Allah does not impose blame upon you for what is unintentional in your oaths, but He imposes blame upon you for what your hearts have earned. And Allah is Forgiving and Forbearing. – Quran 2:225
Ma’arifulul-Qur’an – Maulana Muhammad Shaffi
The above verse has been cited by critics that it allows husband and wife to lie to each other all the time. This is false. The verse is only speaking about those who make ‘oaths’ unintentionally without thinking about what they were saying. The following commentators of the Quran will elaborate further.
The verse warns those who swear in the name of Allah that they will not do some virtuous deeds or that they will not effect a compromise between two groups. The verse reminds them that by this behaviour they using the name of Allah as barrier against the good deeds, which is severe violation of the Sanctity of the name of Allah, and they must avoid it in any case.
The laghw or ineffectual oath has two meanings:
(i) In the first case it means a false oath sworn without volition over something in the past, or it could have been sworn with volition while the oath-taker considers it to be true in his supposition. For example, guided by his information and supposition, one needs up declaration on oath that a certain person has arrived while that person had not arrived in reality. Similarly, if someone swears on oath for something in the future unintentionally, while he has actually wanting to say something else, but the words of oath come out of his lips mistakenly, this type of oath falls in this category. All these three types are not act of sin and that is why they called laghw or ineffectual. This act will not reprehensible in the Hereafter (Akhirah). As compared to this the oath which has been declared reprehensible is the one that has been uttered intentionally knowing it to be false. This is known as ghamus (perjury), and is an act of sin, but according to the Hanafiyyah, it does not require kafarah or expiation. Therefore laghw, in the sense explained earlier, involves no kaffarah more obviously, (because it is not a sinful act). The verse under discussion exclusively takes up these two categories that carry no kaffarah.
(ii) Laghw also means that which has no kaffarah. It will becalled as laghw because it does not entail the liability of kaffarah in this world. Given this meaning, the word, laghw is inclusive of ghamus, which being an act of sin, however, does not require kaffarah. As compared to this, the oath that requires kaffarah is called mun’aqidah (that which is established, confirmed: fait accompli). For instance, if someone intentionally declares on oath to the effect that he or she would not perform a certain act, then, acting contrarily requires kaffarah. (Bayan al-Quran). 
Illuminating Discourses on the Noble Quran – Tafseer Anwarul Bayan – Shaykh Ashiq Ilahi Madni
THE LAWS AND TYPE OF OATHS
Oaths are of there types: The first, called ‘Ghamus’, occurs when a person takes a false oath regarding an action of the past e.g. He swears that he had done a certain action wheras he did not, or vice versa. The Holy Prophet says in a narration of Bukhari, ‘Major sins are polytheism (shirk), disobedience to parents, murder and the ghamus oath’ [Mishkatul Masabih, p17]. The word ghamus is derived from the root word ‘ghams’ which means the complete merging of one thing into another. Certain scholars explain that this particular term is used because such a false oath will cause a person to be submerged in Hell. The second type of oath, called ‘Mun’aqida’, is when a person takes an oath concerning some future action e.eg. he swears that he will do a certain action, or will do do some action. By breaking such an oath, expeditaion (kaffara) will be compulsory (wajib), as is mentioned in Surah Maida. The details regarding the expiation (kaffara) will InShaa-Allah be mentioned there. The third type is when a person takes an oath concerning a past action, being convinced of it truth, whereas it never occurred. This is called ‘Laghw’ (futile oath). The above verse makes reference to this type of oath regarding which a person will not be answerable. According to Sayyidna Aysha … the futile oath is that which is used in common dialogue e.g. ‘Wallah’ (words which are not intended as oaths but resemble them). [Bukhari v.2, p986]
The verse concludes with the statement that Allah is most Forgiving and Clement since He will not require a person to render any account for these unintentional utterances. 
Sayyid Abul Ala Maududi – Tafhim al-Qur’an – The Meaning of the Qur’an
243 We learn from authentic Traditions that if anyone takes a thoughtless oath to do or not to do a thing and afterwards realizes that fairness demands its abrogation, he should abrogate it and expiate for it. The expiation for breaking an oath is the feeding of ten needy persons or clothing them or the liberation of a slave. If one cannot afford this, he must observe fast for three days. (Please see Al-Ma’idah, V : 89).
244There is neither expiation nor any punishment for those oaths that one utters unawares as a by word. 
The Holy Qur’an – Arabic Text With English Translation & Short Commentary – Malik Ghulam Farid
225a. By vain oaths are meant unintentional or thoughtless oaths in ordinary conversation, and by what the hearts have earned is meant an oath intentionally taken.
The Holy Quran – Arabic Text with English Translation, Commentary and comprehensive Introduction [Year 2002 Edition] by Maulana Muhammad Ali, page 100 – 101
273. The word Urdah meaning a butt or an obstacle, it is indeed an act of blasphemy that one should use the name of Allah Who is the Fountain-head of all goodness, to abstain from doing deeds. Again, it is a gross violation of the sanctity of Allah’s name that it should be used as a butt or target for profane or purposeless oaths. This and the following verse serve as sort of introduction to 2:227, in which the subject of swearing to keep away from one’s wife has been pointedly stated.
274. Taking an oath is a serious matter, but some men are in the habit of swearing without meaning anything. Such oaths as are taken thoughtlessly or as a matter of habit or those taken in a sudden fit of anger do not call for expiation. 
 Ma’arifulul-Qur’an By Maulana Muhammad Shaffi volume 1, Page 561 – 563
 Illuminating Discourses on the Noble Quran – Tafseer Anwarul Bayan – By Shaykh Ashiq Ilahi Madni, volume 1, page 282 – 283
 Sayyid Abul Ala Maududi – Tafhim al-Qur’an – The Meaning of the Qur’an http://www.englishtafsir.com/Quran/2/index.html#sdfootnote243sym
 The Holy Qur’an – Arabic Text With English Translation & Short Commentary  By Malik Ghulam Farid Page 90 – 91