Certainty of the call of God is not only necessary for sending you into the ministry; nothing is more essential for keeping you there.  Regardless of the blessings and fruitfulness God grants to your service, there will be dark, heavy days when you would walk away from the Gospel ministry if it weren’t for the bedrock of assurance that you are doing what God Himself has called you to do.  Not having an unshakable sense of divine call is one of the main reasons why so few who begin to preach stay devoted to it for a lifetime.  But preachers who, like Jeremiah, are sure of the fire of God’s call in their bones (Jer. 20:9), can, as Jeremiah did, endure glaciers of opposition and icebergs of discouragement.