Verse 3 mentions “preparing the way,” one that God will be traveling: “make . . . a highway for our God.” This refers to the common practice of monarchs, who, before traveling into a new place, would send a party ahead of them to make sure that the road—the way—was easily passable. This crew would open up difficult passages, level out the road, make sure that it was as straight as possible, and remove any impediments to smooth travel. The Greek historian Diodorus Siculus (Diodorus of Sicily) gives an account of the marches of Semiramis into Media and Persia that illustrates this practice:
In her march to Ecbatana she came to the Zarcean mountain, which, extending many furlongs, and being full of craggy precipices and deep hollows, could not be passed without taking a great compass about. Being therefore desirous of leaving an everlasting memorial of herself, as well as of shortening the way, she ordered the precipices to be digged down, and the hollows to be filled up; and at a great expense she made a shorter and more expeditious road, which to this day is called from her the road of Semiramis. Afterward she went into Persia, and all the other countries of Asia subject to her dominion; and wherever she went, she ordered the mountains and precipices to be leveled, raised causeways in the plain country, and at a great expense made the ways passable.
In the gospels, Isaiah 40:3-4 is quoted in reference to John the Baptist, because this was his calling: He was to prepare the way for the uncrowned Monarch, and he did that by preaching a message of repentance. He told the people how to straighten out their lives to be prepared when the King arrived. He told the multitudes to bear fruits that indicated true repentance and advised them to be willing to share their goods with their neighbors. He warned tax collectors to stop being crooked and not to collect any more than was legally required. He instructed soldiers to stop being crooked through intimidating people, falsely accusing, and being discontent. While John did not actually use the word “crooked,” his message, in essence, was to equalize the areas of their lives that were askew (Luke 3:4-18).
We, too, are looking forward to the arrival of the King, and so we are also called to “prepare the way” within our own lives—though not, like Semiramis, to leave an everlasting memorial to ourselves. Isaiah 40:4 describes the preparation as bringing every valley up and every mountain down to the level of the road. The crooked places have to be made straight, and the rough places smoothed.
However, this prophecy does not say that the King will not arrive until we are ready. Rather, the King will arrive at the appointed time, and whether or not we have straightened our crookedness will determine if we face His wrath or His reward when He does.
We cannot straighten the crookedness of the world, but through God's power, we can straighten our own paths. God has given us the gift of His Word, which will help us to evaluate properly whether something in our lives will make the path crooked or straight. He has given us the example and teachings of the Messiah. He has given us inspired letters. He has given us laws, statutes, judgments, reflections, proverbs, praise, prophecy, and history. He has given us specifics and principles, all of which can be used to help us consider our ways: to consider whether a word or action is sin; whether we are asserting our will against another; whether something will make our path to the Kingdom more difficult; and whether our attitudes, approaches, or activities will make someone else's path crooked.
Another thing that God has given us in His Word is hope—because we can read about the future. We know that when God's plan is complete, nothing will be crooked. God will wipe away every tear; there shall be no more death, nor sorrow, nor crying. There shall be no more pain, for—to paraphrase Revelation 21:4—the former crookedness will have been straightened out. There will be a new heaven and a new earth. There will be new spiritual bodies, and most importantly, new hearts.
God tells us, and shows us, how to be a part of that future. Right now, our responsibility is to make our paths as straight as possible—not just for our sakes, but also for the effect it has on others.