The Church says that the plates are evidence that links the Book of Mormon to the ancient world.
"What Are the Book of Mormon Gold Plates? | Now You Know," April 13, 2020, YouTube, accessed November 29, 2021
The plates are tangible evidence linking the translated Book of Mormon to the ancient prophets who wrote it.
This particular clip begins at 3:30 on the video and can also be found here: https://www.ldsliving.com/new-church-video-explains-the-significance-of-the-gold-plates-and-why-we-still-need-them-today/s/92704