Allah said:
﴿وَلَيْسَ الْبِرُّ بِأَن تَأْتُواْ الْبُيُوتَ مِن ظُهُورِهَا وَلَـكِنَّ الْبِرَّ مَنِ اتَّقَى وَأْتُواْ الْبُيُوتَ مِنْ أَبْوَبِهَا﴾
(It is not Al-Birr (piety, righteousness, etc.) that you enter the houses from the back, but Al-Birr is from Taqwa. So enter houses through their proper doors.)
Al-Bukhari recorded that Al-Bara' said, "During the time of Jahiliyyah, they used to enter the house from the back upon assuming the Ihram. Thereafter, Allah revealed (the following Ayah):
﴿وَلَيْسَ الْبِرُّ بِأَن تَأْتُواْ الْبُيُوتَ مِن ظُهُورِهَا وَلَـكِنَّ الْبِرَّ مَنِ اتَّقَى وَأْتُواْ الْبُيُوتَ مِنْ أَبْوَبِهَا﴾
(It is not Al-Birr (piety, righteousness, etc.) that you enter the houses from the back but Al-Birr is from Taqwa. So enter houses through their proper doors.)
Abu Dawud At-Tayalisi recorded the same Hadith from Al-Bara' but with the wording; "The Ansar used to enter their houses from the back when returning from a journey. Thereafter, this Ayah (2:189 above) was revealed...''
Al-Hasan said, "When some people during the time of Jahiliyyah would leave home to travel, and then decide not to travel, they would not enter the house from its door. Rather, they would climb over the back wall. Allah the Exalted said:
﴿وَلَيْسَ الْبِرُّ بِأَن تَأْتُواْ الْبُيُوتَ مِن ظُهُورِهَا﴾
(It is not Al-Birr (piety, righteousness) that you enter the houses from the back,).''
Allah's statement:
﴿وَاتَّقُواْ اللَّهَ لَعَلَّكُمْ تُفْلِحُونَ﴾
(...and have Taqwa of Allah that you may be successful.) Have Taqwa of Allah, means to do what He has commanded you and refrain from what He has forbidden for you,
﴿لَعَلَّكُمْ تُفْلِحُونَ﴾
(that you may be successful.) tomorrow when you stand before Him and He thus rewards you perfectly.
﴿وَقَـتِلُواْ فِي سَبِيلِ اللَّهِ الَّذِينَ يُقَـتِلُونَكُمْ وَلاَ تَعْتَدُواْ إِنَّ اللَّهَ لاَ يُحِبُّ الْمُعْتَدِينَ - وَاقْتُلُوهُمْ حَيْثُ ثَقِفْتُمُوهُمْ وَأَخْرِجُوهُمْ مِّنْ حَيْثُ أَخْرَجُوكُمْ وَالْفِتْنَةُ أَشَدُّ مِنَ الْقَتْلِ وَلاَ تُقَـتِلُوهُمْ عِندَ الْمَسْجِدِ الْحَرَامِ حَتَّى يُقَـتِلُوكُمْ فِيهِ فَإِن قَـتَلُوكُمْ فَاقْتُلُوهُمْ كَذَلِكَ جَزَآءُ الْكَـفِرِينَ - فَإِنِ انتَهَوْاْ فَإِنَّ اللَّهَ غَفُورٌ رَّحِيمٌ - وَقَـتِلُوهُمْ حَتَّى لاَ تَكُونَ فِتْنَةٌ وَيَكُونَ الدِّينُ للَّهِ فَإِنِ انتَهَواْ فَلاَ عُدْوَنَ إِلاَّ عَلَى الظَّـلِمِينَ ﴾
(190. And fight in the way of Allah those who fight you, but transgress not the limits. Truly, Allah likes not the transgressors.) (191. And kill them wherever you find them, and turn them out from where they have turned you out. And Al-Fitnah is worse than killing. And fight not with them at Al-Masjid Al-Haram (the sanctuary at Makkah), unless they (first) fight you there. But if they attack you, then kill them. Such is the recompense of the disbelievers. ) (192. But if they cease, then Allah is Oft-Forgiving, Most Merciful.) (193. And fight them until there is no more Fitnah (disbelief and worshipping of others along with Allah) and the religion (all and every kind of worship) is for Allah (Alone). But if they cease, let there be no transgression except against Az-Zalimin (the polytheists and wrongdoers).)