One passage the Gap Theorists invariably bring up when talking about Genesis 1 is Isaiah 45:18,
For thus saith the LORD that created the heavens; God himself that formed the earth and made it; he hath established it, he created it not in vain, he formed it to be inhabited: I am the LORD; and there is none else.
Their desperation is really showing here. They bring up that the Lord "created it [heavens] not in vain, he formed it [earth] to be inhabited:" and try to say with a straight face that since God did not create it that way (formless), it must have become that way. Has their Genesis Gap Googles given them myopia? The text in Genesis 1:2 says the earth was "without form" or formless. The text in Isaiah says He "formed it..." Do we have to spell it out for you? The Lord did not intend for the earth to be inhabited until he was finished forming it! In Gen 1:2 the process was just starting and nothing was yet formed. He didn't make man until the sixth day after everything was formed and established!
Furthermore, this verse is talking about God's purpose in creating the heavens and earth; His reasons for wanting a creation to start with. He wants it populated with people. He is not talking about the process of creation. This is similar to a carpenter saying abut a rocking chair he made, "I did not make this chair to be useless; I formed it for a person to sit and rock in."
The Gap Theorists have overextended themselves with this one.
Another "key" passage the Gap Theorists like to bring up is Jeremiah 4:23
I beheld the earth, and, lo, it was without form, and void; and the heavens, and they had no light.
Here we find the same words that are in Gen 1:2. Depending on the stripe of Gap Theorists you may encounter, some insist this is an actual reference to creation (Dake, etc.), but most others will concede this refers to a future judgment on Judah (Jer 4:3, 5) or even the Tribulation.
The context of the passage is the Lord is pleading with Judah and Jerusalem to "Break up your fallow ground...take away the foreskins of your heart, ye men of Judah and inhabitants of Jerusalem: lest my fury come forth like fire, and burn that none can quench it, because of the evil of your doings" (vs 3-4). In vs 22 the Lord states, "For my people is foolish, they have not known me...to do good they have no knowledge." Then speaking as looking back from the future judgment the Lord says He "beheld the earth, and, lo, it was without form, and void...."
Obviously this is a poetic passage where the Lord describes the coming judgment as being so harsh and severe that at least the area of the earth around Judah and Jerusalem will resemble the formless, original state of creation! It is like since man has been continuing to degenerate in understanding and knowledge (vs 22) ever since creation, God is in a sense un-creating the earth as well! Man is reducing himself into moral formlessness so the Lord will reduce the earth into physical formlessness.
However, some of the Gap Theorists will not let the passage rest at that. They feel compelled to find a way to use it to bolster their Genesis Gap claims since it has the words "without form and void" in it like Gen 1:2, but as you will see, their tactics are devious.
The Gap Theorists who profess to be Bible Believers have a dilemma. They so much want "was" in Gen 1:2 to be understood as "became" so they can prove their pre-Adamic earth that they can't sit still. Here is an example of their double talk found in the PDF "Ten Reasons Why The Gap Is A Fact." The author states so he can sound like a Bible Believer,
"No one is advocating here (though some have, we do not) that the Scripture should be changed [from “was” to “became.”]....However, a closer analysis of the definition of “was” (it can mean “be” or “become”) and it's usage in Scripture...opens the door for a broader understanding of Genesis 1.2....But, if we apply the standard definition of the word to Genesis 1.2, we can see that “was” could mean that the earch (sic) became without form and void after it was made perfect in Genesis 1.1." source
Talk about trying to "have your cake and eat it too." This guy right before your eyes changed "was" into "became" while emphatically saying he wasn't doing it!
Jeremiah 4:23 is one of the passages they use to try and hoodwink their readers into thinking "was" is really "became." The reasoning goes like this from The Gap Fact,
Since the earth is obviously not “without form, and void” now, IT WILL BE during the Tribulation [when the author believes Jer 4:23 will occur]. That means that it WASN’T without form and void at one time before God’s judgment “hit.” It will BECOME without form and void.
See where he is going? He says since the "without form, and void" of Jer 4 is in the future it will have to "become" that way since its not that way now. Fair enough, this is common sense, but he can't stop there. He goes on to say,
After that event has taken place [Jer 4:23] IT TOO will be PAST just like Genesis 1:2. That is the “crux” of the interpretation of Genesis 1:2.
Then he uses many words to try and convince the reader that since the events of Jer 4:23 are in the future it will have to become "without form and void" since it is not now, and since Gen 1:2 which uses the same words is in the past now, it must have had to become "without form and void" as well! Have you ever heard such a contrived, convoluted and false argument? They call this "sound doctrine" and "comparing Scripture with Scripture"? It has more holes in it than a screen door!
Just because statements may use some of the same language within them does not mean the state of things in one statement is necessarily true in the other. There are all kinds of differences in the scene of Jer 4 and Genesis Gap. In Jer 4 there are "mountains," "birds," "cities," (missing) "man," etc. In Genesis 1:2 there is only water. The Jeremiah 4 judgment will not be a destruction like the Gap Theorists claim for the Gap. In Gen 1:2 the only physical object present was water yet no Gapist we are aware of believes the land of Judah (or the earth) will again be nothing but water.
The Lord describes Himself what He means by the earth being without form and void in this particular instance in verses 4:24-27,
24, I beheld the mountains, and, lo, they trembled, and all the hills moved lightly.
25, I beheld, and, lo, there was no man, and all the birds of the heavens were fled.
26, I beheld, and, lo, the fruitful place was a wilderness, and all the cities thereof were broken down at the presence of the LORD, and by his fierce anger.
27, For thus hath the LORD said, The whole land shall be desolate; yet will I not make a full end.
He says the land is empty of men and sky of birds; the cities are broken into rubble and the farms turned into a wilderness, and sums it up with, "The whole land shall be desolate...." This is nothing like the situation in Genesis 1:2. (Notice again how earth is the land by comparing vs 23 with vs 27.)
In spite of their similarities, these passages speak of different times and different events and Jeremiah 4 doesn't prove in any way that without form and void in Gen 1:2 is the result of a judgment.