Why is it important that a jury reflect the racial make-up of the community?

It's important for the jury to represent the community so you do not have a one-sided idea of what is going on, also that the person may feel more comfortable with members of their community as well as someone of their same race. Or racial makeup of there community so they see that the jury may understand them better.

necessary and proper clause. the congress shall have power to all laws which shall be necessary and proper for carrying into execution the foregoing powers, and all other powers vested by this constitution in the government of the united states, or in any department or officer thereof.