Al-Fatihah indicates the Necessity of praising Allah. It is required in every Prayer.

The beginning of Surat Al-Fatihah contains Allah's praise for Himself by His most beautiful Attributes and indicates to His servants that, they too, should praise Him in the same manner. Hence, the prayer is not valid unless one recites Al-Fatihah, if he is able. The Two Sahihs recorded that `Ubadah bin As-Samit said that the Messenger of Allah said,

«لَا صَلَاةَ لِمَنْ لَمْ يَقْرَأْ بِفَاتِحَةِ الْكِتَابِ»

(There is no valid prayer for whoever does not recite Al-Fatihah of the Book.)
Also, it is recorded in Sahih Muslim that Abu Hurayrah said that the Messenger of Allah said,

«يَقُولُ اللَّهُ تَعَالَى : قَسَمْتُ الصَّلَاةَ بَيْنِي وَبَيْنَ عَبْدِي نِصْفَيْنِ، فَنِصْفُهَا لِي وَنِصْفُهَا لِعَبْدِي وَلِعَبْدِي مَا سَأَلَ، إِذَا قَالَ الْعَبْدُ:

«الْحَمْدُ للَّهِ رَبّ الْعَـلَمِينَ يَوْمِ إِنَّ اللَّهُ يُؤْمِنُونَ كَفَرُواْ اللَّهُ يُؤْمِنُونَ غِشَـوَةٌ عَلَى الْمَغْضُوبِ يُنفِقُونَ اللَّهُ سَوَآء قُلُوبِهِمْ يُؤْمِنُونَ اللَّهُ عَلَيْهِمْ قُلُوبِهِمْ تُنذِرْهُمْ يُوقِنُونَ اللَّهُ بِالْغَيْبِ سَمْعِهِمْ يُؤْمِنُونَ قُلُوبِهِمْ تُنذِرْهُمْ يَوْمِ أَمْ اللَّهُ لّلْمُتَّقِينَ قُلُوبِهِمْ بِمَآ اللَّهُ يُؤْمِنُونَ إِنَّ اللَّهُ يُؤْمِنُونَ كَفَرُواْ اللَّهُ الْمَغْضُوبِ الرَّحْمَـنِ الرَّحِيمِ»

، قَالَ اللهُ: أَثْنى عَلَيَّ عَبْدِي فَإذَا قَالَ:

[مَـلِكِ يَوْمِ الدِّينِ ]، قَالَ اللهُ: مَجَّدَنِي عَبْدِي، وَإِذَا قَالَ:

[إِيَّاكَ نَعْبُدُ وَإِيَّاكَ نَسْتَعِينُ ]، قَالَ: هذَا بَيْنِي وَبَيْنَ عَبْدِي، وَلِعَبْدِي مَا سَأَلَ، فَإِذَا قَالَ:

[اهْدِنَا الصِّرَاطَ الْمُسْتَقِيمَ ]

[صِرَاطَ الَّذِينَ أَنْعَمْتَ عَلَيْهِمْ غَيْرِ الْمَغْضُوبِ عَلَيْهِمْ وَلاَ الضَّآلِّينَ ]، قَالَ: هذَا لِعَبْدِي، وَلِعَبْدِي مَا سَأَلَ»

(Allah said, `I divided the prayer into two halves between Myself and My servant, one half is for Me and one half for My servant. My servant shall have what he asks for.' When the servant says,

[الْحَمْدُ للَّهِ رَبِّ الْعَـلَمِينَ ]

(All praise and thanks be to Allah, the Lord of all that exists.), Allah says, `My servant has praised Me.' When the servant says,

[الرَّحْمَـنِ الرَّحِيمِ ]

(The Most Gracious, the Most Merciful), Allah says, `My servant has praised Me.' When the servant says,

[مَـلِكِ يَوْمِ الدِّينِ ]

(The Owner of the Day of Recompense), Allah says, `My servant has glorified Me.' If the servant says,

[إِيَّاكَ نَعْبُدُ وَإِيَّاكَ نَسْتَعِينُ ]

(You we worship, and You we ask for help), Allah says, `This is between Me and My servant, and My servant shall have what he asked.' If the servant says,

[اهْدِنَا الصِّرَاطَ الْمُسْتَقِيمَ - صِرَاطَ الَّذِينَ أَنْعَمْتَ عَلَيْهِمْ غَيْرِ الْمَغْضُوبِ عَلَيْهِمْ وَلاَ الضَّآلِّينَ ]

(Guide us to the straight path. The path of those on whom You have bestowed Your grace, not (that) of those who have earned Your anger, nor of those who went astray), Allah says, `This is for My servant, and My servant shall have what he asked.')