“Christian theology teaches the doctrine of prevenient grace, which briefly stated means this, that before a man can seek God, God must first have sought the man.
“Before a sinful man can think a right thought of God, there must have been a work of enlightenment done within him; imperfect it may be, but a true work nonetheless, and the secret cause of all desiring and seeking and praying which may follow.
“We pursue God because, and only because, He has first put an urge within us that spurs us to the pursuit. “No man can come to me,” said our Lord, “except the Father which hath sent me draw him,” and it is by this very prevenient drawing that God takes from us every vestige of credit for the act of coming. The impulse to pursue God originates with God, but the outworking of that impulse is our following hard after Him.” 
“When the great God brought salvation to men, He put it in the form of a message, and according to Paul in the Corinthian epistle, He decreed that men should be saved through preaching. That is, they should be saved through hearing that message. We call that message, the Gospel.
“What was before that? Some theologians refer to this as ‘prevenient grace.’ That is the grace God brings to their hearts before they hear, and before they believe. I don’t know too much about ‘prevenient grace,’ and I don’t think anybody else does. So when you hear anybody expostulating on that learnedly and at length, write him off, because he knows more than the Bible reveals. But there must be some preparation of God in the heart or there would be no believing at all. On the other hand, there isn’t enough preparation to save the man, so he has to hear something.” 
 Tozer, The Pursuit of God (1961, Marshall Morgan & Scott Ltd., London, UK), pp. 11-12
 Tozer, Fellowship of the Burning Heart (2006, Bridge-Logos, Alachua, FL, USA), p. 102