Calling people to repentance isn't the problem.
Placing the emphasis on human will and human activity is the problem.
Scripture says we are dead in our sins. A corpse cannot will itself back to life, the only way a dead person can live is by a supernatural work of God. Lazarus didn't get up and walk out of the tomb by his own strength and power, rather, Christ called out to him and raised him from the dead.
Faith is given to us by God, it's a gift. Nobody can have faith unless God gives them faith. The word must go out and accomplish its goal:
"Faith comes from hearing, and hearing through the word of Christ." - Romans 10:17
It is the Word, Christ's Word, that goes out and comes to us, we who are dead and in the tomb of sin and death, and by its life-giving power raises us to life. This is why we can speak of God's Means of Grace, the Word and Sacraments. In Baptism the Word comes to us, and we are really rinsed and cleansed by the Word which is with the water, and where we were formerly dead and paralyzed by sin--strangers and enemies of God--we are now children and heirs of promise by this adoption of grace.
We didn't do it. God did it, it is God alone who saves.
Christ, who conquered Sin and Death, Tomb, Hell and Devil, this Jesus Christ alone has the power over death, the keys by which to free the captives. And it is His work on the cross, His resurrection power, and the Gospel Word He proclaims to us which does what He sets it out to do. When God speaks it is never in vain.
It was this Word that saved a dying thief on the cross. It was this Word that brought Lazarus back to life. It is this Word that we hear in the proclaiming of the Gospel, both audibly in preaching and tangibly in the Sacraments, that is efficacious and powerful, sharper than any two-edged sword. And this Word brings the dead to life. This Word freely justifies the sinner, reconciling them to God. This Word can do all these things because of the One who speaks it.
But none of our words can do a thing. None of our thoughts, our actions, our ideas. Our most noblest words, our most loft of works, these are like filthy rags and can do nothing to improve our station or status with God.
And the good news is that God doesn't stand high above waiting for us to come to Him. The good news is that God is pro-active, coming down to us. God comes down, God always comes down. God is always the one coming to man, to save him, to love him, to repair what is broken and redeem what is lost. Time and again, throughout all Scripture, it is God who comes down, not man who goes up. Time and again when man tries to go up, he fails--for it is impossible with man, but with God all things are possible.
-CryptoLutheran