What are the reasons for objectification of labor?

I found this: " Alienation of the worker from the act of production (???? what does this mean). By means of commodification (????), the labor power of the worker is reduced to wages (an exchange value); the psychological estrangement (Entfremdung) of the worker results from the unmediated relation (????) between his productive labor and the wages paid to him for the labor. "

Is this the answer, and if so, can you please clarify it for me?