For this is what the fathers did. Although they had a sure promise, they nevertheless did not neglect the means but used their industry and ingenuity in warding off dangers and in the government of their whole life. At the same time, however, they had the Word before their eyes, and in this they trusted when their toil and knowledge did not suffice. For God rules us in such a way that He does not want us to be idle. He gives us food and clothing, but in such a way that we should plow, sow, reap, and cook. In addition, He gives offspring, which is born and grows because of the blessing of God and must nevertheless be cherished, cared for, brought up, and instructed by the parents. But when we have done what is in us, then we should entrust the rest to God and cast our care on the Lord; for He will act (cf. Ps. 55:22).
Thus God could rule the church through the Holy Spirit without the ministry, but He does not want to do this directly. Therefore He says to Peter: “Feed My sheep (John 21:16). Go, preach, baptize, absolve.” In the state He says to the magistrate: “Watch, defend, use the sword, etc.” Therefore Paul calls the apostles “fellow workmen with God” (1 Cor. 3:9). To be sure He alone works. But He does so through us.
Thus God could have made children without Adam, just as at the beginning Adam did nothing at all, since he was formed from the mud of the earth. Nor did Eve do anything, since she was created from Adam’s rib. But later God said: “Be fruitful and multiply” (Gen. 1:28), as though He were saying: “Now with your cooperation I will create children.” This is true in all other actions of our common life. I must not cut the tree down with my nose, but I must take an ax or a saw. The tree must not be cut down with a blade of straw, but with an ax. And this is why God has given man reason, perception, and strength. Use these as means and gifts of God.
This should always be repeated and discussed in the church of God, in order that we may steer a middle course and deviate neither to the right nor to the left. There should be no doubt about the promise; nor should God be tempted by neglecting and underestimating the means ordained by Him.
Luther’s works, vol. 8: Lectures on Genesis: Chapters 45-50