What are the teachings or biblical understanding, why God assigned Lucifer to guard the Holy Mountain?

> You were anointed as a guardian cherub, for so I ordained you. You were on the Holy Mount of God. (Ezekiel 28:14, NIV) God is an all powerful God, the creator of Heaven and Earth both the visible and the invisible. This raises a number of questions ... Why would an infinite and powerful God need a created cherub to guard the Holy Mountain? What is there in the Holy Mountain that needs to be guarded upon and from whom? Are the created angels seen as maybe the subject and the possible intruder to the Holy Mount? Is there a treasure there that the angels might steal? The question I would like answered is: **why is there a need to guard the Holy Mountain of God as all the angels even combined cannot match the infinite power of God?**