Allah is praised with His Attribute of Perfection in the first two verses: for the ayah, “The Most Gracious (Ar-Rahman), the Most Merciful (Ar-Rahim)” reiterates His Attributes of Perfection, to which His response was “My slave has glorified Me”, this is because the Arabic word thana refers to manifold praise that is offered to one who is worthy of being praised for his numerous commendable attributes. Therefore the statement, “Alhamdullilah” “All praise is due to Him” is considered thana and “Ar-Rahman Ar-Rahim” “the Most Gracious (to mankind), the Most Merciful (to believers)” is the attribution of the (praiseworthy) attribute of Mercy to Allah.
When the ayah, “Master of the Day of Judgement” is recited, the slave (of Allah) ascribes to Allah the sole ownership of authority on the Day of Judgement where His Justice, Pride and Glory as well as the truthfulness of His Messengers are manifested, and the reality that He is the true King to whom belong this world and Hereafter. In response to this ayah, Allah says, “My slave has glorified Me” because this manner of praise is called glorification (tamjid) in that it entails praising Allah with respect to His Attributes and Greatness, Glory, Justice and Kindness.
Inner Dimensions of the Prayer by Ibn Qayyim Al-Jawziyyah Pages 40-41