There is nothing in the Bible to suggest a gap in Genesis 1, it is something people put there to try and explain evolution and creation and dinosaurs because they chose to believe men instead of God
Ephesians 1:4 According as HE hath chosen us in Him *BEFORE* the foundation of the world (*AGE*) that we should be holy and without blame before Him in love.
Now this *foundation of the world* is a verb meaning *casting down - overthrow* which is indeed that 'gap' as some like to call it found in Genesis 1:2.
When was Lucifer created and when did Lucifer rebel and when did Lucifer get *cast down*? Genesis give the outline and the other Heavenly PREDESTINED prophets fill in the events but do not give us exact dates.
Now there is a reason why Paul over and over tells about those predestined and even tells us that by doing so Ephesians 1:9 Having made known unto us THE mystery of HIS will.
There is quite a bit in Job describing Lucifer’s fall from heaven when he became Satan, prior to the Garden of Eden.
The gap theory simply looks at different constraints in our understanding of time and places them in a timeline.
As it turns out, there is a remarkable amount of consistency in gap theory from mapping Scriptural timeline constraints with extrabiblical accounts. Although we might not place veracity in various mythologies from different peoples, there remains a remarkable consistency of even their accounts when placed in that same timeline and Scriptural accounts. This led to the study known as Euhemerism back in the early 1900s, which posited all mythologies, as distinct from fable, had some basis in fact.
Since everything we need to perform good works by His standards are provided in Scripture, and Scripture doesn’t explicitly state the gap theory, there is nothing wrong in not placing our priorities on gap theory. On the other hand, Scripture doesn’t tell us about a sizable amount of knowledge which is true, such as quantum mechanics, electrodynamic wave and field theory, etc, but that doesn’t mean such studies are false or not useful tools.
The same might be said for gap theory, in accounting for a large amount of extrabiblical datum.