To preach with authority does not mean that you are loud, can boast several degrees, or show how many books you have published. A man that preaches with authority gets his doctrine form the word of God. He gives glory to God. He feedsthe sheep with knowledge and understanding. He loves like a shepherd and does not threaten like a taskmaster.
Our zeal for the Lord should always be in line with the clear direction of the Lord.
If a man feels led to preach the gospel, he should consider this lesson and be in deep prayer and preparation before he even begins to answer that call. He should continue in prayer and preparation while he carries out God's orders. And it would be a true help to the cause of Christ if his church and family freed his hands as much as possible to the good work.