Is time measurement arbitrary? That is, is the division of trips around the sun into years just something we do?

And God said, “Let there be lights in the expanse of the heavens to separate the day from the night. And let them be for signs and for seasons, and for days and years, and let them be lights in the expanse of the heavens to give light upon the earth.” And it was so. And God made the two great lights—the greater light to rule the day and the lesser light to rule the night—and the stars. And God set them in the expanse of the heavens to give light on the earth, to rule over the day and over the night, and to separate the light from the darkness. And God saw that it was good. And there was evening and there was morning, the fourth day. – Genesis 1:14-19

One of the reasons we mark years and days and (more significantly) weeks is because that’s how God set it up. In making the universe the way he did, in placing the stars where they are, in placing the earth where it is, with the atmosphere it has, on the tilted axis it twirls on, God made it so we could mark years and days. The regularity with with they pass is a testament to God’s faithfulness. Consider,

The word of the Lord came to Jeremiah: “Thus says the Lord: If you can break my covenant with the day and my covenant with the night, so that day and night will not come at their appointed time, then also my covenant with David my servant may be broken, so that he shall not have a son to reign on his throne, and my covenant with the Levitical priests my ministers…” – Jeremiah 33:19-21

The passage of day and night at regular, predictable intervals shows God’s covenant faithfulness to his people and his promises. I think that in the passage above, we are meant to see that faithfulness fulfilled in the coming of Jesus. He is the true Son of David and he is the fulfillment of the Levitical priesthood (Hebrews 8 – 10).

So isn’t it fitting that pretty much globally we are celebrating the beginning of the year 20089 (thank you Sean) Anno Domini, that is The Year of Our Lord?  God made it so that we could mark years and days and be assured of his faithfulness till the “fullness of time” when Jesus was “born of women, born under the law”(Galatians 4:4). And now we number the years since. Amazing.

So why did I say that marking the week is most significant? Because there is no natural marker for a week. Morning and evening, a day. One trip around the sun, a year. Seven days, a week. Why? Because God created the heavens and the earth in six days and rested on the seventh. This pattern was recognized by the Hebrews (Exodus 16) before the law was given (Exodus 20 and following). The Sabbath on the seventh day recognized and solemnified that pattern and, according to Hebrews 4, Jesus fulfilled it in a way and so we rest in him. So even our seven day week is a recognition of God’s promise from the foundation of the world till the coming of Jesus.