"Nevertheless, each one should retain the place in life that the Lord assigned to him and to which God has called him." 1 Corinthians 7:17a - 1 Thessalonians 5:24
Each of us is called to relationship with God through Jesus Christ. We are called by Him, to Him, and for Him. Once we enter that relationship with Christ, we are called into the physical expression of that relationship. This is where our vocations are manifested as a result, not as an end in themselves.
Additionally, there are examples of special callings in the Bible in which individuals have a direct communication from God to do a specific task for Him. Moses, Paul, Peter, and many others had direct communication about what God was calling them to do. Not everyone receives this "special" calling. This is not to say God is not personal with each of us. Some have had extraordinary supernatural encounters with God that led to their calling being specific to a task ordered by God. All of us have been called to follow Christ and live our lives in obedience to Him. Many of us have a sense to go in one direction or another based on our life experiences and giftedness. This, too, is God's calling.
Calling goes beyond our work and includes our relationships to others: our spouse, our children, our neighbors -- and our co-workers. We must remember this in order that our "work calling" does not become elevated at the expense of the other important aspects of our lives. This is the holistic approach to the gospel in which God made all of life equally important.
Therefore, the next time someone says, "I was called into the ministry" or "I am in full-time Christian work," stop him or her and tell him or her we are all in full-time Christian work. There is no secular and religious in the economy of God. I have a dear friend who often says, "I am a servant of the living God masquerading as a dentist." So, too, are you first a servant of the living God.