Some others here started another thread about the Gap idea of Genesis 1 obviously to air out (hot air mostly) their opinions against it, without actually giving anyone a chance to grasp it from Scripture. For those interested, here's a more fair view of it.
General Explanation:
Many Christian scholars and ministers who understand what some call The Gap Theory of Genesis do so not because of trying to reconcile The Bible and science. The idea did not originate from Darwinists or evolutionists either, because the gap idea only supports the idea of God as Creator, NOT theories of EVOLUTION. Those not given to understand it are likely to give it negative associations, just as the ignorant did with our Lord Jesus' Ministry on earth among sinners. It's also important to understand that true scientific discovery will always agree with God's Word, for real science is the study of facts. It's false or pseudo science that confuses the concept of God's creation. We don't have to fear true science, for it won't conflict with God's Word.
Gen 1:1 In the beginning God created the heaven and the earth.
We have the definite article 'the' in front of heaven and earth. Heaven is plural in the Hebrew.
It's assumed by most this first statement serves as a general introductery to every event that follows after it. Like this is what I did, and then here's how I did it. There's no reason to treat the meaning of this verse any other way at this point. But as in many places in God's Word, an introductery statement may take on a whole lot more depth once the detail in the rest of the chapter comes out.
2 And the earth was without form, and void; and darkness was upon the face of the deep. And the Spirit of God moved upon the face of the waters.
This is the first verse in Genesis 1 that can cause one to go back to verse 1 and look at it in a deeper light. Here's why...
The phrase "without form, and void" in the Hebrew is tohuw va bohuw. In Jeremiah 4 this whole phrase appears again, however, in the Jer.4 example it's about a trembling of the already existing earth, a destruction of its surface, turning the earth into a waste, into confusion, vanity. In Isaiah 45:18, God uses the word 'tohuw' to show vanity, something vain, useless, wasted or in a ruin. This word 'tohuw' is translated in other KJV passages also as: confusion, empty place, nothing, (thing of) nought, vain, vanity, waste, wilderness.
In all other examples of this word 'tohuw' in The Bible, it is used in the sense of something that existed going into confusion or a wasted condition. The Hebrew word 'bohuw' (Gen.1:2 as "void") is also translated in that same sense in other KJV usages. You can use a Strong's Exhaustive Concordance and/or Englishman's Concordance to easily confirm that tohuw va bohuw meaning from the Hebrew and in other KJV cases.
This revealing of the meaning of 'tohuw va bohuw' presents two main choices. Is this Gen.1:2 verse about a time before the earth was created, when there was a state of nothingness? Or is this actually pointing to an already created earth back at Gen.1:1 that is being described as having gone into a waste or ruined state at Gen.1:2?
With the phrase "face of the deep", Hebrew 'tehown' ("deep") has very specific usage pointing to waters in the earth. It's used for the waters of fountains of the great deep in Gen.8 during the flood of Noah's day. It's used about God parting the waters of the Red Sea when leading Israel out of Egypt. It's used of springs that come out of the earth. In Ps.104, it used of the depth of waters covering the earth like a garment. In all those Bible cases, it is used in association with an already existing earth. That poses another problem here in Gen.1:2 in thinking the earth is non-existent at this point.
The "face of the waters" is associated with that previous "deep" and time of darkness. These "waters" will be continually mentioned in this first part of Gen.1. As of yet, there still is no direct statement of God creating earth matter beyond Gen.1:1. It is assumed by many that God is creating earth matter at some point here after Gen.1:1. But so far, there's nothing about it beyond Gen.1:1. Instead, Gen.1:2 is declaring the earth is a waste or in a ruined state, with waters affecting it, like a flood covering over the earth.
3 And God said, Let there be light: and there was light.
4 And God saw the light, that it was good: and God divided the light from the darkness.
5 And God called the light Day, and the darkness he called Night. And the evening and the morning were the first day.[i/]
Still nothing about the creating of earth matter here. Darkness was over the face of the waters, and now there is light by God speaking.
6 And God said, Let there be a firmament in the midst of the waters, and let it divide the waters from the waters.
These are the same waters first mentioned back at Gen.1:2. Here God is forming a firmament (sky, cloud, atmosphere), by separating those waters in two. Still nothing about creating earth matter here. Those waters are either suspended in empty space at this point, or the earth was already there underneath those waters since Gen.1:2.
7 And God made the firmament, and divided the waters which were under the firmament from the waters which were above the firmament: and it was so.
8 And God called the firmament Heaven. And the evening and the morning were the second day.
God creates the sky with this act, by parting the waters, taking some of the waters up to form the atmosphere, while leaving the rest of the waters below the sky. Again, either those waters below the firmament were hanging in empty space, or the earth was already there underneath.
9 And God said, Let the waters under the heaven be gathered together unto one place, and let the dry land appear: and it was so.
10 And God called the dry land Earth; and the gathering together of the waters called he Seas: and God saw that it was good.
(KJV)
Here God gathers the waters below the sky into one place, and suddenly dry land appears from underneath. That still is not the specific act of creating earth matter. Instead, it is like those waters were completely covering the earth (like a garment per Psalms 104).
When those Gen.1:1-10 verses are covered in accordance with other Scripture evidences, it suggests that God first created the heavens and the earth back at Gen.1:1 as written, and then at Gen.1:2 something happened to the earth that caused it to be covered by a flood of waters, much like how the flood of Noah's day covered the whole earth to destroy the wicked off the earth.
If Gen.1:2 is indeed pointing to a destruction upon the earth by waters of a flood, then that would suggest that in between Gen.1:1 and Gen.1:2 there was an indeterminable time period only God knows how long. That's where the idea of a 'gap' of time comes from. It would mean that starting at Gen.1:2 forward, God is renewing the earth because of something that happened in between verses 1 and 2. It then becomes impossible to determine just when God originally created the earth.