Ministry is the pursuit of God-given vision, and as such, it is a race. And it is not, just a race, but a marathon race, which involve exchanges of batons by the runners.
The point here is this, there is hardly anyone called into the ministry with an assignment, which no one has ever had in the past.
Hence, when God calls anyone into the ministry, he calls him or her after an order. Thus, an orderless call is a symptom of its futility. When God calls a person, he assigns him or her responsibility after a given order, and such a fellow is expected by divine ordination to serve or minister by the order.
There was in the days of Herod, the king of Judea, a certain priest named Zacharias, of the division of Abijah. His wife was of the daughters of Aaron, and her name was Elizabeth. And they were both righteous before God, walking in all the commandment and ordinance of the lord blameless. But they had no child, because Elizabeth was barron, and they were both well advanced in years. So it was that while he was serving as priest before God in the order of his division.
Luke 1: 5 -8
The verse 8 above shows that God never expect anyone to minister without order. While doing the work of an apostle, prophet, evangelist, pastor and teacher, God expect you to function after an order.
The scripture talks about Elisha operating after the order of the double spirit of Elijah, and John coming after the order of Elijah. Jesus was said to have been a Priest by God forever, according to the order of Melchizedek (Hebrews 7:17). So, you must know your own order of call and you must function from it. For there lies your source of effectiveness in ministry.