Let me first say that I am not a "Scofield" "gaper". I don't personally believe that Genesis 1:1 details the original creation. It details the "new world" that is several thousands years old in its current form. So I don't officially believe in a "gap" between Genesis 1:1 and Genesis 1:2. HOWEVER, many of the arguments that are made for the "gap" theory fit my beliefs.
I am going to list a few that are universally recognized.
1. God is perfect and everything he does is perfect, so a newly created earth from the hand of God should not have been without form and void and shrouded in darkness. Deuteronomy 32:4, Isaiah 45:18 1 John 1:5. Not to mention the unlikely scenario that God's first action in creation couldn't have been to "form" a mass without notable, distinguishing features. Nor would he simply form an "sphere" of "water", "covered" in "darkness". In Him is Light and there is no "darkness" at all. Thus, "darkness" would indicate prior "judgment".