In The Name of Allaah, The Most Merciful, The Bestower of Mercy.

 Allaah [The Most High]:

يَا أَيُّهَا الَّذِينَ آمَنُواْ أَطِيعُواْ اللّهَ وَرَسُولَهُ وَلاَ تَوَلَّوْا عَنْهُ وَأَنتُمْ تَسْمَعُونَ

وَلَا تَكُونُواْ كَٱلَّذِينَ قَالُواْ سَمِعۡنَا وَهُمۡ لَا يَسۡمَعُونَ

O you who believe! Obey Allaah and His Messenger, and turn not away from him [i.e. Messenger Muhammad] while you are hearing. And be not like those who say: “We have heard,” but they hear not. [Surah al-Anfaal Aayaat 20-21]

[يَا أَيُّهَا الَّذِينَ آمَنُواْ أَطِيعُواْ اللّهَ وَرَسُولَهُ – O you who believe! Obey Allah and His Messenger]: Meaning: [Obey Allaah and His Messenger] by fulfilling what they have commanded and keeping away from what they have forbidden. [وَلاَ تَوَلَّوْا عَنْهُ وَأَنتُمْ تَسْمَعُونَ – and turn not away from him (i.e. Messenger Muhammad) while you are hearing]: Meaning: Do not turn away from obedience to Allaah and obedience to His Messenger, whilst you are hearing what is been recited to you from the Book of Allaah [i.e. the Qur’aan, Allaah’s commands, admonitions and advices]- because turning away will place you in the most perilous situation. [وَلَا تَكُونُواْ كَٱلَّذِينَ قَالُواْ سَمِعۡنَا وَهُمۡ لَا يَسۡمَعُونَ – And be not like those who say: ‘’We have heard,’’ but they hear not]: Meaning: Do not suffice with claims that are devoid of reality, for it is something displeasing to Allaah and His Messenger. Eemaan is not wishful thinking and merely adorning oneself with it [outwardly]; rather it is that which firmly settles in the hearts and is affirmed by one’s deeds.  [Source: (Tayseer al-Kareem ar-Rahmaan Fee Tafseer Kalaam al-Mannaan). slightly paraphrased]

Consequences of disobeying Allaah and His Messenger

http://www.salaficentre.com/2015/07/allaah-afflicts-mankind-with-different-types-of-afflictions-because-of-their-disobedience-and-wicked-deeds/

Repentance

https://www.salaficentre.com/2012/03/abridged-the-best-way-to-seek-allaahs-forgiveness-with-comments-from-imaam-bin-baaz-rahimahullaah/

https://www.salaficentre.com/2016/08/salaah-tawbah-prayer-repentance/

http://salaficentre.com/wp-content/uploads/2015/08/obligation1.pdf