Explanation
Translated from Ustadz Firanda Andirja's Indonesian commentary (Bekal Islam). Quoted verses, hadith and duas keep their Arabic; where the commentary gave its own Indonesian rendering of them, that rendering is not translated and is marked [translation not shown].
Allah is Most Great in His essence and His attributes, and Allah is greater than everything other than Him in every aspect of perfection. Thus
First: Allah is the Greatest in His lordship (rububiyyah), that is, Allah is Most Great in His essence; the universe is truly very small in Allah's grasp. Likewise, Allah is Most Great in His creating, His owning, and His governing. Truly, none can create as Allah does, and Allah's governing of the universe and of all things is perfect compared with the way creatures govern what they manage. His laws and His shari'ah are perfect, unlike the laws of creatures, which constantly undergo change and deficiency and can only apply in particular times and places.
Second: Allah is Most Great in His names and attributes. That is, in every attribute of perfection, Allah is the most perfect. The attributes of creatures, whether angels, jinn, or humans, are all full of limitation and deficiency, unlike the attributes of Allah, which are perfect.
Third: Allah is Most Great in worship, so nothing is worshipped and submitted to as Allah is.
So when a person is praying, he magnifies Allah in his heart and makes all creatures small in his breast, so that he can concentrate as he begins his prayer, which is a direct connection between himself and Allah.
REFERENCE
Quoted as the source gives it, in Indonesian.
(1)H.R. Bukhari no 744, Muslim no 598, H.R. An Nasa-I dalam assunanul kubro 1/466 no 971