Therefore, it is necessary to censure the foolishness, or rather, the ungodliness, of those men who refer all things to predestination, which embraces the hidden counsels of God and His government unknown to us.12 If you were God, it would be permitted to proceed according to this. But because God wants you to be ignorant of this, therefore remain in your calling and within the limits of the Word, and use the means and counsels which God has ordained. I cannot foresee the fruit of my doctrine, namely, who is to be converted and who not. If I now wanted to say: “Those who are to be converted will be converted without my efforts, and if some are not to be converted, what point is there in my toiling to no purpose?” this would be absurd and impious. For who are you to ask this question? Do your duty and leave the outcome to God. It is not for you to say: “If these things are to happen, they will happen.” In His Word God has issued instructions through Paul saying: “Go and do your duty! Preach the Word; be urgent in season and out of season, censure, beseech, rebuke in all patience and doctrine” (cf. 2 Tim. 4:2). This commandment must necessarily be obeyed, idle curiosity being disregarded.
Luther’s works, vol. 6: Lectures on Genesis: Chapters 31-37 p 105