Isaiah 54:16 is a passage from the Book of Isaiah, found in the Old Testament of the Bible. It is the number on the license plate of Smith's car in The Matrix Reloaded.
The passage reads,
"Behold, I have created the smith who blows the fire of coals, and produces a weapon for its purpose. I have also created the ravager to destroy;"
The passage is a reference to Smith, the chief agent tasked with hunting down members of the human Resistance in The Matrix, and who later became "unplugged" after he was destroyed by Neo at the end of that film. In the sequels, The Matrix Reloaded and The Matrix Revolutions Smith was a free agent who was able to copy himself much like a computer virus and spread throughout the Machine City, however, he is once again destroyed by Neo in a final showdown.