What God asks us to do is not set in stone for a lifetime. In other words, the urgency for a particular act of service may not be the same tomorrow. For some of my retired clergy friends, it is hard to accept the possibility that God could release them from the call placed on their lives at the beginning of ministry and lead them into a different era of service. It does not mean that the call to serve Christ which we all embrace at our baptism is ever lifted, but simply to say that His expectations of what that means for us may change through the course of the years.
I never thought I would be content with a life empty of preaching, but have discovered an awareness of usefulness through writing and what I would have at one time described as pastoral acts. I have numerous friends who at an earlier age traveled all over the world as mission team members, but have found that the urgency of that calling has been lifted for other things. Recently, I visited with a friend who spent the better part of his life directing choirs only to experience God's leading toward becoming one who plans worship services for his church instead of maintaining a music ministry.
The thing of which we should not be afraid is change. What we have done in faithful obedience to God's call on our life may be part of His preparation for the next season. Both Isaiah and Jeremiah started ministry as priests, but ending up wearing the mantle of a prophet. David was anointed to be a king, but is best known for a body of spiritual literature which still stirs our souls. What God wants us to be about today may change as tomorrow comes. We need not fear. We simply need to do what we have done since the beginning which is to go with Him in faith.