45:18 formed the earth. Note that the Lord “formed” the earth, He “made” it, He “established” it, He “created” it. He did it Himself!
45:18 not in vain. Since the word here for “in vain” is the Hebrew tohu, this verse has been made the main proof text (actually pretext!) for the so-called “gap theory,” which attempts to add billions of years of the history of the earth and its inhabitants in a supposed gap between the first two verses of Genesis. Genesis 1:2 says that “the earth was without form”—that is, tohu—so the argument is that since Isaiah says God did not “create” the earth tohu, it must have “become” tohu in a great cataclysm that climaxed and terminated the geological ages. However, this is an impossible theory geologically, since these ages are based entirely on a supposed uniform continuity with present geological processes, and there is no place in the geological ages for a global cataclysm that would leave the earth without form and void. The main purpose of the gap theory is to avoid conflict with geologists over the age of the earth, but it squarely contradicts them on their basic premise of uniformitarianism. Such a worldwide cataclysm as proposed by proponents of the gap theory would so disintegrate and rearrange the crust of the earth as to leave no evidence of any previous ages. The gap theory would thus accommodate the geological ages by destroying all the evidence for them! This is why no geologist, Christian or otherwise, believes the gap theory.
45:18 to be inhabited. The thrust of this verse is that God had a definite purpose for the earth. He created, established, made, and formed it as a habitation for man. When initially called into existence by God, it was “unformed and empty,” as stated in Genesis 1:2, but God did not intend to stop there. He took six days to prepare it for man in order to set a pattern for man’s work week (Exodus 20:8-11); the earth was not “perfect,” in the sense of being “finished,” until God said so, at the end of the six days (Genesis 2:1-3).