In The Name of Allaah, The Most Merciful, The Bestower of Mercy.
Allaah [The Most High] stated:
الْحَمْدُ لِلَّهِ رَبِّ الْعَالَمِينَ
مَالِكِ يَوْمِ الدِّينِ
All the praises and thanks be to Allah, the Lord of the ‘Alamin (mankind, jinns and all that exists). The Most Beneficent, the Most Merciful. The Only Owner (and the Only Ruling Judge) of the Day of Recompense (i.e. the Day of Resurrection)”
This (statement) comprises of the first fundamental principle, and that is to know The Lord, His Names, His Attributes and His Actions. The Names mentioned in this Soorah are the basis of all the (Perfect and Exalted) Names, and they are ‘Allaah’, ‘Ar-Rabb’ and ‘Ar-Rahmaan’. 
The Name ‘Allaah’ comprises of the Attributes of Al-Uloohiyyah. Al-Uloohiyyah’, meaning: The One described with Absolute Greatness, which makes Him the Only One deserving of being a true deity and no one else has a share in this alongside Him. He is the One described with all attributes of absolute perfection—Attributes of perfect Loftiness, Greatness, Beauty, Mercy, Benignity and kindness, Generosity and Beneficence. And due to this, He is the only one worthy of being deified and worshipped, because He alone possesses the attributes of Absolute Perfection and Glory.
He alone has the right to be deified because He (alone) is singled out with the Attribute of absolute Self-sufficiency. He is not in need of anyone, whilst everything else is absolutely in need of Him and dependent on Him. He (alone) is singled out with the attribute of perfect Lordship and He is the Nurturer of all that exists. He alone deserves to be deified because He (alone) is the possessor of absolute perfect Sovereignty and Authority. He alone is the One singled out with the attribute of Perfect Mercy and He alone bestowed all hidden and apparent blessings to His creation. He alone is worthy of being deified because He is the only One that encompasses everything with His perfect Knowledge, Decrees, Wisdom, kindness, Mercy, Power and Might, and everything in the heavens, the earth and what is between them are overwhelmed and subdued by Him and He is never overcome. Nothing happens in the entire existence except by His will and there is not a single creature that possesses the ability to benefit or harm except by His will. He alone has the right to be deified because He alone is singled out with the attributes of absolute self-sufficiency in every way, whilst all other things are absolutely in need of Him at all times and in every aspect (of their existence). All things are absolutely in need of Him in seeking to establish the necessary beneficial affairs in their lives, and they are always in need of His provision and all the sources leading to its facilitation. They are always greatly in need of Him, whilst He is never in need of them.
‘Ar-Rabb’: The Name ‘Ar-Rabb’ [The Lord and Nurturer] embraces the Attributes of Lordship. He is the Nurturer of all the creation with His blessings. He (alone) prepared for the (creation) every perfection and beauty suited for it, and He prepared what they need. He gave everything the nature suited for it, and then He guided every creature towards what (i.e. the purpose) it was created for. He bestowed abundant blessings to His slaves; made them thrive and nurtured them with the most perfect nurturing. His Lordship and Nurturing are through two ways:
Firstly: His absolute Lordship over all His creation and taking care of them, whether they are pious or impious. He (alone) created and provided for them, and He (alone) is the One in absolute control of their affairs. He (alone) granted them all blessings and He has no partner in all of this.
Secondly, His special nurturing of His friends: He nurtured them with Eemaan and servitude to Him. He gave them knowledge of [‘Marifatu Allaah -knowledge and aware of Allaah] and made it flourish through their constant turning to Him in obedience; avoiding disobedience to Him; depending upon Him and fleeing to Him for refuge. He removed them out of darkness and entered them into light; facilitated ease for them and prevented difficulty from them. He facilitated every good for them and preserved them from every evil. 
‘Ar-Rahmaan’: The Name Ar-Rahmaan (The Most Beneficent) comprises of the attributes of kindness and Generosity  The Names ‘Ar-Rahmaan’ (The Most Beneficent), ‘Al-Barr’ (The Most Benign and Kind), ‘Al-Kareem’ (The Bountiful, the Generous One Abundant in Good), ‘Al-Jawaad’ (The Munificent, Bountiful), ‘Ar-Ra’oof’ (The Compassionate and Kind) and ‘Al-Wahhaab’ (The Bestower): All these Names (of Allaah) are close to one another in meaning, and they all describe The Lord with the Attributes of absolute perfect Mercy, Benignity and kindness, Munificence and Generosity, and a (description of) the vastness of His Mercy and bestowal (of blessings) to all the creation in accordance with His perfect Wisdom. He specified for the believers amongst them (i.e. the believers amongst Mankind and Jinn) with an abundant share. He (The Most High) said: [وَرَحْمَتِي وَسِعَتْ كُلَّ شَيْءٍ ۚ فَسَأَكْتُبُهَا لِلَّذِينَ يَتَّقُونَ – And My Mercy embraces all things. That (Mercy) I shall ordain for those who are the Muttaqun (the pious ones)]. [Al-Araaf: Ayah: 156].
All blessings and kindness come about as a result of His Mercy, Munificence and Generosity. All the goodness of the worldly life and afterlife are a result of His Mercy. 
[مَالِكِ يَوْمِ الدِّينِ – The Only Owner (and the Only Ruling Judge) of the Day of Recompense (i.e. the Day of Resurrection)]. Imaam Ibnul Qayyim (rahimahullaah) said: It necessitates affirmation of the hereafter and reward for the slaves for their good and bad deeds; single out The Lord (i.e. Allaah) with the right to judge between the creation and because of the fact that He (alone) judges with (absolute perfect) justice. All of this comes under His statement: [مَالِكِ يَوْمِ الدِّين -The Only Owner (and the Only Ruling Judge) of the Day of Recompense (i.e. the Day of Resurrection)(6)].” The One who possesses the Attributes of Absolute Sovereignty, incomparable Greatness and Majesty, subduing and administering the absolute disposal of the affairs of the creation, gives commands and recompenses etc. (7)
 Al-Fawaa-id, page:41]; Fathur-Raheemil Malikil Allaam Fee Ilmil Aqeedah Wat-tawheed wal-akhlaaq wal-ahkaam of Imaam sadi (rahimahullaah): Abridged page:12]; Fathur-Raheemil Malikil Allaam Fee Ilmil Aqeedah Wat-tawheed wal-akhlaaq wal-ahkaam of Imaam sadi (rahimahullaah): Abridged page:39-40]; Al-Fawaa-id: page:41];  Tayseer Kareem Ar-Rahmaan Fee Tafseer Kalaam Al-Mannaan Al-Allaamah of Imaam As-Sadi(rahimahullaah) 5/621. Abridged];  Badaa-I At-Tafseer Al-Jaami Limaa Fassarahu Al-Imaam Ibnul Al-Jawziyyah. Vol 1. Page 33]; Dr Saaleh As-Saaleh (rahimahullaah)]