As an evangelist—even as someone who has been preaching over twenty five years—there are topics that are off limits for me to address as a guest speaker. This is especially true of a young man at the beginning of his ministry. I made the mistake of addressing issues beyond my experience and knowledge when I first started preaching. And it cost me valuable relationships that I never regained.
Just because something is in scripture doesn't mean that everyone is qualified to address it in every congregational context. Yes, every preacher is to "preach the word" (2 Timothy 4:2), but not every preacher should preach every word. There are some biblical topics that it takes experience to be able to effectively communicate them. One example for me was the doctrine of "trusting God." I was raised to not go to doctors or take medicine for any reason. I am not bashing that, I am simply making a point. But as an 18 year old preacher who had barely been sick a day in his life, I was not the person to be preaching to seasoned saints who were struggling with serious diseases that they were not "trusting God" because the sought medical help. There are plenty other applicable examples, but this will suffice.
Also, there is a relationship with people that is required in order to be able to address certain issues in their lives. There are some church topics and issues that only a pastor is qualified to address. For example: if I preach against something that a pastor allows, then I have helped no one. I undermine the spiritual authority of that congregation. I cast doubt on the spirituality and judgment of that pastor in front of his people. I alienate myself from the congregation. No good can come from it. If God wants to use me to affect theological change in a church I do not pastor then he will open the door for private discussion with the man who is the pastor. If in private conversation the pastor asks my opinion and his view changes, then he will communicate that change to his congregation. It is not my responsibility to sabotage him in his own pulpit.
Young man if God blesses you to speak in any pulpit, then speak basic doctrine, faith and life. Encourage and strengthen the congregation and pastor. If you have something deeper to say, then trust God to provide the proper relationship and maturity for you speak it.