He is shy. He lives in reclusion. Isolated. Has no social contacts. Like a clam in a shell. You invite him (/ask him) to come out of this imaginary shell and talk to others.

The Longman dictionary of contemporary english gives the following definition... "come out of your shell" to become less shy and more confident and willing to talk to people. An example: "She's really come out of her shell since she went to college. P.S. I used to think that "shell out" is a short form of the expression "come out of one's shell" LOL However, "shell out" means to pay a lot of money for something, especially unwillingly, like in "If you want the repairs to be done right, you'll have to shell out at least $800." Don't make my mistake :)))

Howdy "come out of his shell" it means you become more interested in other people and more willing to talk and take part in social activities, and if someone brings you out of your shell, they cause you to do this "come out of your shell" to become less shy and more friendly cowboy...

the meaning is to be bold and daring

became apparent or showed oe even exoteric