Here's why:

* Transcription is the process of creating RNA from DNA. RNA is a single-stranded molecule, while DNA is double-stranded.

* The template strand serves as a guide for the RNA polymerase enzyme. This enzyme reads the template strand and builds a complementary RNA strand.

* The other strand of DNA, called the non-template strand or coding strand, has the same sequence as the RNA transcript (except for thymine being replaced with uracil in RNA). However, it's not directly used in transcription.

So, while both strands of DNA contain the genetic code, only one strand is used as a template for RNA synthesis during transcription.