What is the function of 就是
就 has many meanings, In different context, '就是' could mean 'is exactly' ; 'then it is' ; 'just/ only'

Example:


他最怕的话题[就是]关于爱情的话题 = The topic he afraid the most, [is exactly] the topic about love
讨论完关于工作的话题, 接下来[就是]关于爱情的话题 = Finished discussing the topic about job,  next [then it is] the topic about love
他什么书都看，[就是]关于爱情的他不看 = He read any kind of book, [just/ only] the ones about love he doesn't read