[TBC: The Gap Theory is the idea of a great gap in time between Genesis:1:1 and Genesis:1:2, devised to accommodate the evolutionary age system of billions of years of supposed earth history in the Genesis record of creation.]
An argument of those who advocate the ‘gap’ theory is that the word ‘darkness’ suggests that something is wrong with the creation. But Isaiah:45:7 says that God created the darkness. In order for there to be day and night, which was necessary for the further activity of God and man upon the earth, there must be day and night. So God actually had to create darkness. Thus there is nothing implicitly wrong with it being dark. God created it that way. Darkness later came to represent, in some contexts, a symbol of evil—as opposed to light—since ‘God is light and in Him is no darkness at all’ (1 John:1:5). But in the context here there is no evil connotation suggested.
Theologically, there is also a very grave difficulty with the ‘gap’ theory. The Bible says there was no sin or death until man brought them into the world. According to the ‘gap’ theory, however, there had already been billions of years of suffering and death in the world, represented by the fossils and the sedimentary rocks of the earth’s crust, which are supposed now to identify the geological ages. According to the ‘gap’ theory, at the end of the geological ages Satan sinned and was cast to the earth and then there was a great cataclysm, so that the geological ages with billions of years of suffering and death took place before Satan sinned and certainly before man sinned.
The Bible, on the other hand, says specifically that ‘by one man sin entered into the world, and death by sin’ (Romans:5:12), so that there was no death in the world until man brought sin into it. The ‘gap’ theory would require billions of years of suffering in the world before man or even Satan had sinned, and that means that God Himself would be directly responsible for sin in the world. God could not be the author of sin. So the ‘gap’ theory is precluded theologically.
—Henry M. Morris (October 6, 1918 – February 25, 2006, American young Earth creationist, Christian apologist, and engineer. Considered by many to be "the father of modern creation science.”)