"A man had two sons . . .” was a common way to begin a parable, especially one comparing good and bad sons. Matthew uses it to contrast one son, who promises to work in the vineyard but never shows up, with another, who at first adamantly refuses to go to the vineyard but later repents and goes (21:28-32). Which one did the will of his father, asks Jesus? Not the one who talked a good game, but the one who actually followed through with obedient actions.
God will forgive my sins,” quipped Heinrich Heine on his deathbed. “It’s his job.” How different are the viewpoints of Isaiah, Paul and Luke! They note an ongoing theological tension between the assurance of God’s kindness and the call to immediate repentance. Yes, God is merciful, not punishing as we deserve, not automatically correlating our misdeeds with disasters. But there is no room for complacency: if we think we’re standing, we should watch that we do not fall.