We are apt to forget the mystical, supernatural touch of God. If you can tell where you got the call of God and all about it, I question whether you have ever had a call. The call of God does not come like that, it is much more supernatural. The realization of it in a man’s life may come with a sudden thunder-clap or with a gradual dawning, but in whatever way it comes, it comes with the undercurrent of the supernatural, something that cannot be put into words, it is always accompanied with a glow. At any moment there may break the sudden consciousness of this incalculable, supernatural, surprising call that has taken hold of your life – “I have chosen you.” The call of God has nothing to do with salvation and sanctification. It is not because you are sanctified that you are therefore called to preach the gospel; the call to preach the gospel is infinitely different. Paul describes it as a necessity laid upon him.
-Chambers, “The Consciousness of the Call”, My Utmost for His Highest
school stuffs is starting to equal life stuffs.