Yesterday I posted some of my thoughts related to the desire to enter the pastorate. Some have asked me (and others balked) about this idea of being "called" by God to the ministry. I will clarify a bit here and point you to some good resources along the way. First let me say that all Christians are commanded by God to "proclaim his excellencies" and be his "witnesses" to the world. All Christians are called by God to serve the church. The topic here is the divine call to the ministry of the pastorate. This is not a "fuzzy feeling," nor any punctiliar experience where one initially becomes aware of their place in ministry. That may or may not happen to people who are called by God to serve as pastor. By divine calling I do mean that God internally convicts men to give their lives to serving and leading the church as pastor. Charles Bridges pointed out that it is the combination of the internal call (God working in a man's spirit, making him aware of what God has made him to do/be) and the external call (the church's affirmation of God's call) that finally sets a man apart for the ministry. You can read this in Chapter 6 "The Want of a Divine Call a Main Cause of Failure in the Christian Ministry" in his classic work, The Christian Ministry.
Charles Spurgeon also believed that only those men who have sense of divine calling should enter the ministry, and that without it we find our way into danger.
When I think upon the all but infinite mischief which may result from a mistake as to our vocation for the Christian pastorate, I feel overwhelmed with fear lest any of us should be slack in examining our credentials; and I had rather that we stood too much in doubt, and examined too frequently, than that we should become cumberers of the ground. There are not lacking many exact methods by which a man may test his call to the ministry if he earnestly desires to do so. It is imperative upon him not to enter the ministry until he has made solemn quest and trial of himself as to this point. His own personal salvation being secure, he must investigate as to the further matter of his call to office; the first is vital to himself as a Christian, the second equally vital to him as pastor. As well be a professor without conversion, as a pastor without a calling. In both cases there is a name and nothing more. Lectures to My Students, pg. 23.
In the same chapter, "The Call to The Ministry," Spurgeon goes on to explain how a man can determine if he is called by God to the ministry. He explains that such a man will have an "intense, all-absorbing desire for the work," the ability to do the work, bear fruit in the work, and receive the affirmation of the local church.
Sure the internal call is subjective and experiential, but I am okay with that because 1) I am no deist; I believe God convicts and leads his people, and 2) the inward call works in tandem with the local church's recognition.
I agree with Spurgeon who believed it wise to say, "Do not enter the ministry if you can help it." But if you are called you cannot help but "aspire to the office."
For a concise and very good treatment of this topic check out Al Mohler's article Consider Your Calling.