Here's why:

* mRNA carries the genetic code: mRNA is a messenger molecule that carries the genetic code from DNA in the nucleus to the ribosomes in the cytoplasm.

* Ribosomes are protein factories: Ribosomes are the cellular machinery responsible for protein synthesis. They read the genetic code in mRNA and use it to assemble amino acids into polypeptide chains, which then fold into functional proteins.

So, in essence, mRNA acts as a blueprint for the ribosomes to follow when creating proteins.