I have been asked to address a gathering of youth this fall to challenge them to prayerfully consider what God's call on their lives might be. The young person who invited me had attended a worship service where I was the guest speaker earlier this year, and in the message I mentioned that many churches were failing to challenge their young people in this manner. Almost every person I know who is in the ministry today is serving in that capacity because someone challenged them to consider if God might be calling them to do that. Personally, I felt called to the ministry as a youth but did nothing about that until a pastor challenged me again when I was in my mid-twenties.
Growing up in Baptist churches I remember every service ended with an invitation which usually consisted of four parts: salvation, rededication, transfer of membership from another church, and responding to a call of God to "full-time" Christian service. I still often hear the first three as part of the invitation in the churches I visit, but I seldom hear the fourth one any more. BTW - That needs now to be changed to full-time or bivocational ministry since God is now calling many to a bivocational role.
Many persons now serving in pastoral or missionary roles are nearing retirement age. My personal opinion is that a large number may have already retired if the economy wasn't so bad. A number of denominations have aggressive new church planting goals they want to reach over the next few years. Due to the economy and the stress of ministry, a large number of clergy leave the ministry each year. While most studies indicate there are still sufficient numbers of clergy for our churches, that may not be the case in the near future. It certainly is not the case now for smaller churches as many current clergy will not serve in such churches. The need for bivocational ministers to serve these churches is great now and only expected to increase.
You and I cannot call anyone to the ministry. That must be the work of God in a person's life. But, we do have the responsibility to challenge people to consider if God may have such on call on their lives. We can talk with persons we believe demonstrate pastoral gifts at work in their lives about ministry and offer to pray with them as they seek God's guidance in that area. We can give them some pastoral tasks to see how well they do and what that feels like to them. After my pastor asked me to seek God's will in this area he invited me to go with him on pastoral visits when appropriate. One day he handed me a spare key to his study and told me to feel free to use it and his library any time I wanted to study. With my love of books that was almost confirmation by itself that God wanted me in the ministry!
One of the tasks of a leader is to identify future leaders and help develop them for the work to which God has called them. What a loss to the Kingdom of God if there are people in our churches God is calling into the ministry and we fail to help them identify that call.