Who are the 144,000 witnesses?

Every Friday, I answer a common question related to the end times. Today’s is about the identity of the “144,000 witnesses” mentioned in Revelation 7:4.

Question:

I’ve heard you use the term “Jewish” for the 144,000 witnesses in Revelation 7. I've been told by some Jewish friends that “Jewish” means “from the tribe of Judah,” whereas Revelation 7 indicates that the witnesses will come from the 11 other tribes as well. Can you elaborate on this?