Vulnerability can be described as a “willingness to allow one’s weakness to be seen or known; willingness to risk being hurt or attacked.” In a mental image, I’ve heard it described as “giving somebody a knife, turning around, and trusting them not to stab you in the back with it.”
As I was thinking through 2 Corinthians 12:9-10, I made the connection that there is a difference between our traditional understanding of vulnerability, with what I think this short passage is evoking of a Christ-focused vulnerability