This is the 6397th most frequent Polish word.
błażej
"Błażej" is a Polish male given name, equivalent to "Blaise" in English.
Here, 'Błażej' is used as a proper noun, being a person's name, and it's the subject of the sentence.
Błażej kupił nową książkę.
Błażej bought a new book.
In this sentence, 'Błażeja' is the name 'Błażej' in the genitive case, used to indicate association or belonging.
Czy pamiętasz Błażeja z ostatniej imprezy?
Do you remember Błażej from the last party?
Here, 'Błażejem' is the instrumental case of the name 'Błażej', used after the preposition 'z' which denotes accompaniment.