It is the glory of the gospel of God's grace that it provides for this incongruity. God's call, since it is effectual, carries with it the operative grace whereby the person called is enabled to answer the call and to embrace Jesus Christ as he is freely offered in the gospel. God's grace reaches down to the lowest depths of need and meets all the exigencies of the moral and spiritual impossibility which inheres in our depravity and inability. And that grace is the grace of regeneration...God effects a change which is radical and all-pervasive, a change which cannot be explained in terms of any combination, permutation, or accumulation of human resources, a change which is nothing less than a new creation by him who calls the things that be not as though they were, who spake it and it was done, who commanded and it stood fast. This, in a word, is regeneration.
John Murray - Redemption: Accomplished and Applied