Yet man does not find out or discover what God has done, etc. That is: Man cannot know, even if he torments himself, when God wants to do him good, when He wants to start or to stop, just as no one, regardless of how he works at it, can investigate or identify the hour when someone is to be born, to live, or to die. Therefore one should say: “Lord, it is up to Thee to give future things; meanwhile I shall enjoy the life that is present and that has already been given by Thee.” Thus also the other activities of life which he has just cataloged lie outside the power of man. For if this were placed in the hands of men, many would always be waging war, while others would always be playing or building; for there are many who labor at this. The whole world is ours. Only let us not prescribe to God the time or the method of using it. “I refuse to be measured by your counsels,” says God; “otherwise everything will belong to you, including Me.” (Luther’s Works, v.15 p.54)

Scripture speaks about Christendom very simply and in only one way….

The first way, according to Scripture, is that Christendom means an assembly of all the people on earth who believe in Christ, as we pray in the Creed, “I believe in the Holy Spirit, the communion of saints.” This community or assembly means all those who live in true faith, hope, and love. Thus the essence, life, and nature of Christendom is not a physical assembly, but an assembly of hearts in one faith, as St. Paul says in Ephesians 4[:5], “One baptism, one faith, one Lord.” Accordingly, regardless of whether a thousand miles separates them physically, they are still called one assembly in spirit, as long as each one preaches, believes, hopes, loves, and lives like the other. So we sing about the Holy Spirit, “You have brought many tongues together into the unity of faith.” This is what spiritual unity really means, on the basis of which men are called a “communion of saints.” This unity alone is sufficient to create Christendom, and without it, no unity—be it that of city, time, persons, work, or whatever else it may be—can create Christendom.” (Luther’s Works, v.39, p.65)

Also he has given the world into man’s heart, yet so that he cannot find out what God has done from the beginning to the end.

This is a confirmation of the preceding. “Although God has given the world into the hearts of men,” he says, “they still cannot govern it by their own counsels.” “To give into the heart” or “to speak into the heart” is a Hebraism for giving or speaking in a sweet and flattering way. He wants to say: God not only gives the world into the hand of men, so that they can use the things that are present, but also into their heart, so that they can use them joyfully and with pleasure and so that they have fun and delight from it. Nevertheless, man cannot know what the beginning or the end of the work is, when or for how long he is to have these things. Therefore man should be content that he has the world for his use. Paul speaks in similar terms in Acts 14:17: “Yet He did not leave Himself without witness, for He did good and gave from heaven rains and fruitful seasons, satisfying their hearts with food and gladness.” And elsewhere (1 Tim. 6:17): “Who richly furnishes everything.” This happiness the Christian has, and everyone else would have it also if he could be content with the things that are present. St. Jerome says correctly in his preface to the Bible: “The believer has a world of riches, but the unbeliever does not have a penny; as the proverb says, ‘the miser lacks not only what he does not have but also what he does have.’” (Luther’s Works, v.15 p.53)