When God calls us, what does this mean? Os Guinness in his book The Call writes, "Calling is the truth that God calls us to himself so decisively that everything we are, everything we do, and everything we have is invested with a special devotion, dynamism, and direction lived out as a respond to his summons and service."
Here's the "nuts and bolts" of this--as I see it. First, there's a distinct difference between calling and vocation. The lines have been muddied, but the truth is that there's a difference between these two. (I will explain more later.) Second, every Christian is called by God. We must never forget that we are not called to a specific activity, rather, we are called to obedience to Christ. Third, the response to God's calling upon our life is our service. Whatever our vocation--whatever we do in life, should be a direct response to the call of God.
So, there's a primary calling and a secondary calling.  The primary calling is that all should follow Christ, that we should love God with everything we have and everything we do. The secondary calling is how we live in our lives in response to this primary calling. In other words, our every day lives should be a clear response to God's primary call upon our lives to follow Christ. Guinness writes, "The truth of calling means that for followers of Christ, 'everyone, everywhere, and in everything' lives the whole of life as a response to God’s call." 
It seems today that many have separated what they do--their vocation--from their faith. It's not too late to allow God's call in your life to infiltrate your every day life.
 Os Guinness, The Call: Finding and Fulfilling the Central Purpose of Your Life (Thomas Nelson, 2003), 29
 Ibid., p. 31
 Ibid., p. 31