Why would you send a copy of the instructions in DNA versus sending the actual DNA molecule?

DNA is copied because it cannot fit through the nuclear membrane and travel down to the ribosome.

So it is transcribed (translated) to messenger RNA (mRNA). The mRNA can fit through the nuclear membrane and travel down to the ribosome where proteins can be made.

This is why we cannot send the entire DNA molecule itself, it is simply too big to fit. This is why mRNA is extremely important for amino acid production.