Plagiarism is an especially a strange concept when we dive into the pool of Biblical interpretation. My theologian brothers and sisters in academia may not like to hear this, but at the end of the day it may be so.
This is especially a question when we approach Scripture with the belief that there is one true interpretation of most passages. To give one person the credit for the correct interpretation of a passage seems to grant them perhaps too much authority and comes close to ranking them next to the original author.
Is it really possible for any of us to claim ownership of ideas found in the Scripture? Or is it more likely that all of us should claim ownership of what is in the Bible? I’m in favor of citing sources and giving honor to those who went before, but in truth every good idea is built on thousands of years of good ideas...and several bad ones as well.
If we had to cite every one responsible for our own limited intelligence displayed in a single message it would sound like the listing of possible negative side-effects read off during a pharmaceutical commercial, and the sermons would be just as interesting.