I often get the question of whether I think books like 1 Enoch are canonical. I tell people I don’t — and that the question doesn’t matter. A book doesn’t need to be canonical to be useful, or to inform theological thinking. It’s quite evident the NT writers had the content of 1 Enoch and other non-canonical books floating around in their heads. They read them, and those books at times helped them articulate some point in their own letters, or molded their thinking. By way of illustration, if I read Calvin’s Institutes and his commentary on Romans, and then wrote my own Bible study guide about the meaning of the book of Romans, it would be impossible to not have Calvin in my head (no matter how predisposed I was to what Calvin said). Saying the New Testament writers were intellectually divorced from, and uninfluenced by, this material is dishonest and, frankly, uninformed.
For proof, check out this link (hat tip to Matthew for this): New Testament Allusions to Apocrypha and Pseudepigrapha.
The material at the link is also available in a PDF I created: