Mathematician and physicist, Blaise Pascal, once said:
“What else does this craving, and this helplessness, proclaim but that there was once in man a true happiness, of which all that now remains is the empty print and trace?
"This he tries in vain to fill with everything around him, seeking in things that are not there the help he cannot find in those that are, though none can help, since this infinite abyss can be filled only with an infinite and immutable object; in other words by God himself.”
The idea behind the "God-shaped hole" is that each person has a void in his life/soul/spirit that can only be filled by the one true God of the Bible. No matter what else a person may try, nothing else fits correctly in this space. Only a growing, maturing relationship with the God of the Bible, through His Son Jesus Christ, can satisfactorily fill the "God-shaped hole" in each person for this life and throughout eternity.
Though we may try to fill this space with other things, such as philosophy, hobbies, other people, or other beliefs, nothing fits right except for God. The Bible describes our natural hearts as "deceitful" and says we are unable to completely understand it (Jeremiah 17:9). Solomon writes that our hearts are full of evil and contain madness (Ecclesiastes 9:3). Romans 1:18–23 says we humans attempt to worship just about anything other than God, and Romans 8:7 says our natural mind is hostile to God, not wanting to submit to Him and His ways. When we seek to fill our own hearts through human pursuits, we are ultimately left empty and wanting.
It is true that in human pursuits, we may find some contentment and even happiness. After all, God did design us for life on earth. But it is only in Him that our earthly activities and relationships best fulfill their purpose. These things could never give meaning to our lives as God can, but in God, our earthly pursuits are a valid and necessary part of living a meaningful life. When we look to earthly things, or even other humans, to fill our "God shaped hole," we find that they don't fit quite right and are usually quite temporary.