How Halal is turned into Haram :The Three Forms
There are three forms in which something made Halal (lawful and good) by Allah could be declared as Haram (unlawful and evil): (1) BELIEF-WISE, that is, something is taken to be Haram by believing it to be so. (2) VERBALLY, that is, something is taken to be Haram for oneself by saying so for instance, someone swears that he will not drink cold water, or would not eat such and such Halal food, or would not do something which is permissible. (3) PRACTICALLY, that is, someone who neither believes nor says anything, yet decides in practice that he or she would abandon something Halal for ever.
1. Under the first situation, if that thing being Halal stands confirmed by absolute proofs, then, the person who takes it to be Haram shall become a disbeliever (kafir) because of that open contravention of the Divinely-ordained law.
2. And under the second situation, if someone has made something Haram for oneself by declaring it with words of oath, the oath will become effective. There are many words of oath details of which appear in Fiqh books for example, someone clearly says: ' I swear by Allah, I will never eat that' or 'by Allah, I will not do that' or one might say, 'I make taking this or doing that Haram for me.' The rule which governs such actions is that taking such oaths unnecessarily is a sin. If taken, one must break the oath and make amends by paying the Kaffarah (expiation) of that oath, the detail about which will appear later.
3. The third will be a situation in which no Halal has been made Haram either by belief or word of mouth, but practically what one does is similar to what is done with something Haram, that is, takes it as obligatory to abandon it for ever. The rule in this case is: If one takes the abandonment of the Hala1 to be an act of Thawab (merit, reward), then, it is Bid'ah (innovation in established religion) and Rahbaniyah (monasticism) which is a grave sin as categorically laid down (Mansus) in the Qur'an and Sunnah; and acting against it is Wajib (necessary as an obligation); and adhering to such a restriction is an act of sin. Of course, if such a restriction is not there with the intention of Thawab, instead, it is there for some other reason, such as, some physical or spiritual sickness because of which one abandons something permanently, then, there will be no sin in doing so. Reports about some noble Sufis and other pious elders that they had abandoned some Hala1 things are all included under this third kind as they had found them to be harmful for their desiring self, or were advised by a pious elder to abstain from it as harmful in their case which they abandoned as a treatment and remedy. If so, it does not matter.
The Correct Attitude towards Halal Things
At the end of the first verse (87), it was said: وَلَا تَعْتَدُوا ۚ إِنَّ اللَّهَ لَا يُحِبُّ الْمُعْتَدِينَ that is, 'and do not transgress the limits set by Allah because Allah does not like such transgressors.' Here, transgressing means that one abandons something Halal, without any valid excuse, as an act of Thawab. This is something an ignorant person takes to be Taqwa, fear of Allah, while, in the sight of Allah, that is transgression, which is impermissible. Therefore, it was said in the next verse (88): وَاتَّقُوا اللَّهَ الَّذِي أَنتُم بِهِ مُؤْمِنُونَ that is, '(eat from the good and pure sustenance Allah has blessed you with) and keep fearing Allah whose believers you are.
Stated clearly in this verse is that leaving off good and pure things as a source of Thawab (reward) is no Taqwa Rather, quite contrary to that, Taqwa lies in using them as the blessings of Allah and showing one's gratitude for them. However, if something is abandoned as a curative measure against a physical or spiritual disease, that does not count here.
لَا يُؤَاخِذُكُمُ اللَّهُ بِاللَّغْوِ فِي أَيْمَانِكُمْ وَلَـٰكِن يُؤَاخِذُكُم بِمَا عَقَّدتُّمُ الْأَيْمَانَ ۖ فَكَفَّارَتُهُ إِطْعَامُ عَشَرَةِ مَسَاكِينَ مِنْ أَوْسَطِ مَا تُطْعِمُونَ أَهْلِيكُمْ أَوْ كِسْوَتُهُمْ أَوْ تَحْرِيرُ رَقَبَةٍ ۖ فَمَن لَّمْ يَجِدْ فَصِيَامُ ثَلَاثَةِ أَيَّامٍ ۚ ذَٰلِكَ كَفَّارَةُ أَيْمَانِكُمْ إِذَا حَلَفْتُمْ ۚ وَاحْفَظُوا أَيْمَانَكُمْ ۚ كَذَٰلِكَ يُبَيِّنُ اللَّهُ لَكُمْ آيَاتِهِ لَعَلَّكُمْ تَشْكُرُونَ
Allah does not hold you accountable for what is not countable from among your oaths, but He does hold you accountable for the oath you have bound yourself with. Its expiation is to feed ten poor persons at an average of what you feed your family with, or to clothe them, or to free a slave. And whoever finds none shall fast for three days. That is expiation for your oaths when you have sworn. And take care of your oaths. That is how Allah makes His signs clear to you, so that you may be grateful. 
Sequence of Verses
Mentioned earlier was the taking of Halal things as unlawful. Since statements to this effect are sometimes sworn, therefore, the injunction about taking of oaths follows in the present verse.
Three Forms of Oaths and their Injunctions
1.Some forms in which oaths are taken have been described in this verse. Some have appeared in Surah al-Baqarah as well (Ma'ariful-Qur'an, Volume I, Verse 2:225, pages 562-563). The gist of all these is that false swearing about a past event knowingly is, in the terminology of Muslim jurists, Yamin-Ghamus (disasterous oath) for instance, if a person has done something, and he knows that he has done it, and then he knowingly swears that he has not done it. This is false swearing, a grave major sin the curse of which falls in the present life and in the life-to-come. Bat, there is no Kaffarah (expiation) necessary for it. Taubah (repentance) and Istighfar (seeking forgiveness from Allah) are, however, necessary. That is the reason why the Muslim jurists call it the disasterous oath. Ghamus literally means that which drowns. This kind of oath drowns man into sin and its curse, a disaster for one's present and future life.
2. The second form is that someone declares on oath that a past event was true, as based on his knowledge, while it was actually false for example, he learnt from someone that a certain person has come and trusting him, he declared on oath that the person has come, then, he came to know that this was contrary to what had actually happened. This is called Yamin Laghw (ineffectual oath), that which is not counted. Similarly, if a word denoting oath, such as 'by' or 'I swear,' comes to be said unintentionally, that too is known to be what is 'ineffectual oath.' It brings neither Kaffarah (expiation) nor sin.
3. The third form of oath is that one declares on oath that he would or would not do something in the future. This is known as al Yamin al-Mun'aqidah (Binding oath). The rule which governs it is that, in the event the oath is broken, Kaffarah (expiation) becomes necessary and under some situations, it brings sin as well, while in some others, it does not.
At this place in the present verse of the Qur'an, 'Laghw' (ineffectual, not counted) obviously means the oath which brings no Kaffarah (expiation) whether a sin, or not; because it has been mentioned in contrast with : عَقَّدتُّمُ الْأَيْمَانَ (the oaths you have bound yourselves with). This tells us that the accountability (Mu'akhadhad) mentioned here is only the accountability in the present world which comes in the form of Kaffarah (expiation).