I assume that with your question you mean the call to be a preacher or pastor.
All callings in this life are God’s. Too often we elevate one calling above another. Though some callings have more influences in reaching other people yet each calling is contributing to the people around us. It is a very worthwhile thought from Luther when he taught ‘that God milks the cow through the milkmaid.’ Such a task seems not so important and to call that a calling sounds exaggerated. Yet is not exaggerated; it is Biblical. In each Biblical calling God is carrying out His work of providence or grace. Keep this in mind in whatever Biblically acceptable work you are doing. It is as one man who was a repair man in our local school, “I don’t work for the school; I work for my King.” And that put a smile on his face nearly every day I saw him work.
The calling of the ministry is a calling that goes beyond the work of God’s providence. In ministry we are dealing with the work of God’s grace, particularly in the preaching ministry. God gathers His elect and nourishes His Kingdom through the preaching of the Word. A preacher speaks on behalf of God, as an ambassador. No one should intrude himself into that task without having a Divine warrant from God. For how could anyone assume to become an ambassador for a nation without having been ‘called or appointed’ by the government? So we need to be clearly called by God before we move toward the ministry.
How does God a man to the ministry? Many books are written about this subject. Consult The Christian’s Reasonable Service by Brakel. He has an excellent chapter about this subject. Preachers and PReaching by Lloyd Jones is also very useful. John Newton’s collection of letters also has a letter covering the question.
In brief, God doesn’t call a person to the ministry before He has called him in grace. In other words, before we can become one of God’s ambassadors, we need to be one of His children. How else can someone proclaim Him Whom He does not know personally or has no experience of the work of the Holy Spirit in salvation. Besides, he needs to be matured believer. Paul warns TImothy not to put a novice in the office of elder or deacon.
God in His providence also equips the person whom He intends to be a preacher. Gifts such as skills to speak, to lead, to connect with people, to listen and above all to learn. Having said that, some of the Lord’s eminent servants didn’t possess the greatest speaker abilities and personal skills. Paul wrote that he wasn’t among the Corinthians with great eloquence. Perhaps he wasn’t a very good public speaker. But did that matter? When I was in high school, I continued to fail my public speech classes. Still God directed me to become a teacher and through that experience I finally overcame my fears to speak in public. Along with these various gifts, comes the strong desire to be in the ministry. I believe that God kindles this flame of desire in the heart and often does that even before the call to the ministry has come.
But the most important element of the call is that you sense God’s Word directing or calling you to give yourself to the ministry. You need to wait on God in prayer and listen to His Word to know whether it is His will that you go forward in the ministry. You need to be personally convinced of where and what God has spoken to you. I am thankful to this day for my former pastor. When I was considering whether God was directing me to the ministry, I shared with him my thoughts and burden. WHen I asked him what his thoughts were, he simply said, “Thank you for sharing but I have nothing to say. You need to convince me that you are called of God. If you are not completely sure, don’t enter into the ministry.” At the time I didn’t appreciate his answer and wisdom. Later I did thank him for his reply. It sent me back to God and His Word to know from Him whether it was His will.