Byzantines didn't "become more Greek than Roman". They were already Greek to start with.
But anyways... lets not have me rant about that part.
The population was Greek. The empire was split into West and East. West centered on Rome (before the fall) and the East on Constantinople (A town in Greek). From the division working language was Greek.
Greek language and couture was more prevalent in the Eastern Roman Empire. When the fall of the West Byzantine court held onto the Latin language for official decrees and other state documents, but eventually even that was lost to the grater Greek influence.
Hoped this helped! Remember to change this to your own words. <span />
Justinian I.
Explanation:
The Roman have had their own unique set of laws that they implement on all new territories that they have conquered. Everyone had to obey these laws and respect them. The problem was that as the society was becoming more and more developed the Roman laws started to gradually lose sense or to be badly formatted for the changed circumstances, thus creating lot of confusion.
Justinian I decided to change this. He took the Roman laws, sorted them out properly and in accordance to the needs of the people and the state. He then changed some and also implemented some new ones. All in all, Justinian managed to create a better organized, more developed, practical, and modern set of laws. He created the Justinian Code.
International influence, also they had just defeated Spain when they begun having imperial ambitions, therefore they may want to fill that gap
