Be diligent to present yourself approved to God, a worker who does not need to be ashamed, rightly dividing the word of truth.
But shun profane and idle babblings, for they will increase to more ungodliness."
2 Timothy 2:14-16 (NKJV)
What if you were interested in learning about the history of England, but you only read books about the history of Norway? The obvious answer is that you would not learn much, if anything, about the history of England. And what if you wanted to learn how to be a good cook, but the only thing you searched for on the Internet was stories about people who climbed mountains? Again, you would not learn anything about the desired subject. To learn about a certain subject, you have to focus on that subject.
There are three letters in the New Testament that were written to ministers:1 & 2 Timothy and Titus. When I read these letters, it always stands out to me how often Paul talked about avoiding the wrong kind of teaching, and arguments about things that do not really matter. To be successful in ministry, and to be a mature believer, we need to feed ourselves on God's Word and avoid things contrary to the Word. While I realize that this sounds extreme to some people, it is still the truth.
In 2 Timothy 2:15, Paul talks about being diligent to correctly interpret the Word of God. If we spend more of our time focusing on things that are not Bible based than we do with Bible truth, we are going to have problems. Paul says how the wrong kinds of things will "ruin the hearers" and "increase to more ungodliness", which is obviously bad. Focusing on the truth and avoiding the wrong kind of teaching is very important; the things we spend our time with will do something for us, either positively or negatively.