What makes a novel "a classic? Discuss

I think all the classic novels that I read have a few things in common. First, they are written in somewhat poetic ways. The authors use many imagery and vivid details. Second, these books have themes that are not familiar at the time the books were published. The themes shock the readers at first because they are so untraditional ways of writing books. However, these books influence other writers to write in similar styles or techniques, in addition to similar themes. To sum this up, classic novels are the ones that are written with great details, have shockingly new themes, and influence other authors to write similar themes.