This piece of advice is courtesy of CFW Walther, from the introduction to "Law and Gospel."
I want you to come breathing a silent prayer in your heart that God may grant us His Holy Spirit abundantly, that you would profitably hear, and that I would effectively teach.
"Law and Gospel" is a series of Friday night lectures that Walther gave to seminarians preparing for the parish ministry. Walther believed and taught that in order to read the Bible properly, one must be able to distinguish between the two great message in the Bible - law and Gospel. These lectures are required reading for Lutheran pastors - not just once but throughout their ministry. Failure to get law and Gospel straight will leave listeners confused regarding the gift of their salvation which is given by grace alone through faith alone in Jesus Christ alone without any works or efforts of our own.