The answer I am about to give will offend some of my Christian brothers but here is my understanding. First of all, the Bible teaches that God accomplished creation in six days. On the seventh day He rested from His labors. So now we’re down to six days to accomplish the task.
Because we believe that God was doing the creating, and He is, after all … God, it is entirely possible that He did this in six days … literally. Except the Bible doesn’t say that exactly. It uses the word day, but does that mean a 24-hour unit of time? Elsewhere, David, inspired by God to do his writing declared “A thousand years are like a day in your sight.” The ancient Hebrews also spoke of a day as a general description of time and here the suggestion is that what man calculates as a thousand years is only the rough equivalent of a day as God might measure it. In this interpretation God could have taken as many as six thousand years to accomplish the work of Creation.
Elsewhere we hear day used as a description of a season or an era of history as in the days of Elijah. The length of time to which that refers because we have the reference point of the historical record of Elijah and his ministry. Unfortunately for us there is no historical record of the time of Creation for which we can assign a specific number of years to it … like thousands or millions. So that avenue of interpretation seems closed to us if we want to be true to the scriptures as a record of the work of God. That position would make a whole lot of people more comfortable with at least the time normally assigned by evolutionary theory, but that simply reminds us that the Bible does not profess to be a book of science. It is a book of the work of God, which by definition cannot be tested in a tube or in a carbon dating chamber or under a microscope.
For Christians trying to be faithful to God’s Word, the surest statement is this … God created the heavens and the earth. What we have is no accident nor mindless evolutionary process. It is not natural selection. It is intelligent design accomplished at the hand of God as an expression of His goodness and love. The selection comes via a supernatural involvement in nature that creates dependable Laws of Nature to sustain that creation and all of us creatures who inhabit it. It is a Creation that always had humanity in mind, and intended humanity to be the crowning part of that Creation.