God chooses each of us to be used according to His will. As the creator of us all it is His prerogative. In Romans 9:21 it is not saying some people are worth more than others: Does not the potter have the right to make out of the same lump of clay some pottery for noble purposes and some for common use? Paul is simply saying that God, as the creator, has the right to use us uniquely for His purpose. The value of each of us is the same in His eyes.