Why did jace bring Simon through the portal in idris in City of Glass by Cassandra Clare?

In "City of Glass," Jace brings Simon through the portal to Idris primarily to protect him and ensure his safety. Simon, being a mundane, is vulnerable in the dangerous circumstances surrounding the conflict between the Shadowhunters and Valentine. Jace feels a sense of responsibility for Simon, as he is Clary's best friend, and wants to keep him close while navigating the perilous situation in Idris. Additionally, he hopes that being in Idris will help Simon understand the world Clary is part of.