The creation of light on day one was necessary to form the light half of the day. Notice that the dark half preceded the light. (See verse 2). If a day consists of 24 hours, and the evening (dark portion) precedes the morning (light portion), then the “first day” (v. 4) must have begun with the dark portion. This is precisely what we find. If verse 2 describes the earth in its infant state of “darkness”(i.e., first 12 hours), followed shortly thereafter by the creation of “light” in verse 4 (i.e., last 12 hours), then Genesis teaches a young rather than a prehistoric earth!
As an aside, I did a study once on the mystery of this “light”God created on day one after a pastor in Chile challenged our group of missionaries from the U.S. with the following question: “What was the light spoken into existence on day one, and what happened to it once God created the heavenly lights on day four?”Many answered that it was the presence of Christ. But that didn’t seem plausible since it implied that Christ was absent in the evenings! And why would God have to declare the light “good” if it was the glory of His presence? The most plausible answer is that it was simply spoken into existence to serve a temporary purpose, namely, to divide the darkness, thereby creating a 24-hour cycle for the first three days. AfterGod created the “lights in the firmament of the heaven”on day four, He simply recalled the light. Keep in mind that God needs no object to emanate light. God’s spoken Word has the power to create something out of nothing. “The entrance of Thy Word giveth light”(Ps. 119: 130). “God calleth those things which are not as though they were” (Rom. 4: 17).His Word alone is the source! Hebrews 11: 3 tells us: “Through faith we believe that the worlds were framed by the Word of God, so that things which are seen were not made of things which do appear.”This is the how of creation:“And God said…”“He spoke and it was done” (Ps. 33: 9).