The call to ministry is both subjective and objective.
One must, of course, have a desire to minister to God’s people in this capacity and Paul says that such a desire is a good thing (1 Tim. 3:1). Gone are the days in which a young John Chrysostom could be placed into such a position against his will. Certainly the providence of God was at work considering how mightily he was used of God in his time and culture but most would agree his experience should be the exception and not the rule.
There must, however, be some objective validation of one’s internal sense calling. In the passage cited above, the desire to serve is followed by a list of qualification, implying that not everyone should serve in this capacity. A person may feel called and have honorable intentions but simply not be gifted or qualified to serve in such a capacity. Those who have served as ministers can usually provide a good assessment of whether or not the candidate is both qualified and capable of serving. Seeking and successfully completing some measure of theological education is also a good indicator since someone in pastoral ministry must be a teacher and to be a teacher one must first (a) be teachable himself as well as (b) be trained to carry out the functions and duties specific to this role. If one cannot persevere in this, one should consider his sense of calling.
But what if one senses a call but his call is not validated by his church or he is prevented from pursuing the call vocationally? There are other capacities in which to serve and he should make every effort to use his gifts in the service of the church. I have known men who felt a sense of calling but were prevented from pursuing the requisite education or were disqualified due to some other hindrance. Instead of becoming bitter because they did not get their way, they viewed it as God’s providence and sought to study and become good leaders and teachers in their congregations. Some of these men have been very influential in the spiritual lives of their congregations and are used mightily by God. Who is to say they have not made as much if not more impact on the kingdom than they would have had they been ordained?