يَـٰٓأَيُّهَا ٱلنَّاسُ كُلُواْ مِمَّا فِى ٱلۡأَرۡضِ حَلَـٰلاً۬ طَيِّبً۬ا وَلَا تَتَّبِعُواْ خُطُوَٲتِ ٱلشَّيۡطَـٰنِ‌ۚ إِنَّهُ ۥ لَكُمۡ عَدُوٌّ۬ مُّبِينٌ O إِنَّمَا يَأۡمُرُكُم بِٱلسُّوٓءِ وَٱلۡفَحۡشَآءِ وَأَن تَقُولُواْ عَلَى ٱللَّهِ مَا لَا تَعۡلَمُونَ O (سورة البقرة:۱۶۸۔۱۶۹)

"O PEOPLE, EAT OF WHAT IS IN THE EARTH, PERMISSIBLE AND GOOD, AND DO NOT FOLLOW IN THE FOOTSTEPS OF SATAN; INDEED, FO YOU HE IS AN OPEN ENEMY. HE ONLY ORDERS YOU EVIL AND IMMODESTY, AND THAT YOU ALLEGE ABOUT ALLAH WHAT YOU DO NOT KNOW." (SURAH AL-BAQARAH:168-169)

(One of the wrong practices of the non-believers of Arab was that they had declared some things Halal and Hara'am by their own opinion, without any divine guidance. For example, they believed it was permissible to eat a dead animal, while they had declared Halal animals Hara'am. These verses were sent to refute those wrong beliefs and practices.)

The true meaning of the root word "حلَّ " (halla) is 'to open a knot'. In that sense, something being declared Halal means that a knot has been opened and the restriction has been lifted. The blessed Companion Hazrat Sahl ibn Abdullah RAA has said, "Salvation depends on three things - 1. eating Halal, 2. fulfilling (divine) obligations and 3. following the Sunnah of the Holy Prophet ﷺ."

The word "طیّب" (Tayyib) means 'good' as inclusive of the mean and the pure, and covers the twin aspects of being lawful, permissible or Halal and being naturally desirable. 

The word "سوء" (Su) in "ٱلسُّوٓءِ وَٱلۡفَحۡشَآءِ" means something which bothers somebody good and reasonable. The word  "فحشاء" (Fahshae) covers what is immodest. 

The expression "إِنَّمَا يَأۡمُرُكُم" (he only orders you) means instilling a suggestion in the mind. This has been further elaborated upon in a Hadith narrated by the blessed Companion Hazrat Abdullah ibn Masud RAA who said that Rasool Allah ﷺ has said, "The son of Adam is influenced by a suggestion from the Satan and a suggestion from the angel. The Satanic suggestion has the effect of bringing forth the expedient gains in evil deeds and thereby opening the avenues of negating the truth, while the angelic suggestion has the effect of the heart becoming content and satisfied with the promise of success and reward on good deeds, and validation of what is correct."

From Ma'ariful Quran, by Mufti Muhammad Shafi RE