If we could convert ourselves, when would we want to do so? Perhaps we would say: “Not today, but tomorrow. Not this year, but next year. Not now in my youth, and as long as I am healthy, but when I become old and sick.” Because we can do nothing for our conversion and God alone must do everything, we should think, as soon as God begins to work in us, Now, now is the time! For it can happen that if God wants to convert us today but we prefer to wait until next year, God might not be willing to accommodate us, but would instead suddenly and unexpectedly tear us out of this life in our unconverted state to His severe judgment. Then we would have waited too long and we, past saving, would perish. Therefore, Scripture says: “Do not be deceived: God is not mocked” (Galatians 6:7). No one can excuse himself with his powerlessness. When we cannot come to God, He wants to draw us to Himself. When we cannot take God into our heart, He will open our heart for us. When we cannot be rightly frightened of hell, He will work this fright in us.
But whoever then remains in his sins and unrepentance makes himself obdurate. He then will cry out when he goes to hell.
God Grant It: Daily Devotions from C. F. W. Walther p 257