The debate between those who believe God created the universe and those who believe in the naturalistic theory of evolution continues. There are some, believers in God, who do not think that this topic should be discussed as much as it is. They believe that there are other, more important, things (such as the Gospel) that should occupy our time and energies. Are they correct? Is defending the historicity of the Book of Genesis a waste of time? Or is it foundational to one’s understanding of our existence and our understanding of the Gospel message?
Genesis introduces us to God and informs us of what our correct relationship with Him is supposed to be. Ken Ham writes, “Since God made all things, all things belong to the sovereign Ruler and serve to glorify Him (I Chronicles 29:11; Psalm 19:1-4; Isaiah 48:11-13; Revelation 4:11)”  Genesis clearly teaches us that God is the Sovereign Creator of the universe and we are His creations. We were created to love and worship Him and, when we fail to do so, we are living in sin. The entire backstory of who we are is contained in Genesis . If we fail to understand how we have fallen from what we were created to be, we cannot truly understand our desperate need of a Savior.
The theory of evolution threatens one’s perception of the authority of the Bible
The theory of evolution has convinced (brainwashed) many that science has concluded there is no reason to believe in God; rather, the existence of the universe and everything can be explained by naturalistic processes. This is the reason that Christians must continue upholding Genesis as absolutely true; the only other option is to acknowledge some authority, other than the Bible, as our ultimate source of truth.
Dr. R. Albert Mohler, president of Southern Baptist Theological Seminary, says this:
Peter Enns, one of the most frequent contributors to BioLogos, suggests that we have to come to the understanding that, when it comes to many of the scientific and historical claims, the writers of Scripture were plainly wrong. 
It is a question of authority: Do we believe God or do we believe fallible human theories? Either God created everything, including us, or He did not (as secular science would have us believe)…it cannot be both.
Naturalism undermines God’s standard for how humanity should live (what is sinful, what is not), leaving us to decide for ourselves, using our sin-stained hearts and minds, what is right and what is wrong. This is why we are seeing an increase in immorality today. There is no foundation for morality apart from God. If we are merely the result of chemical processes and material substance there is no reason for us being moral people. It is illogical to assume that morals (not to mention thought, logic, truth, justice, love, etc.) originated from a rock or some other inanimate object. Therefore, if one subscribes to the naturalistic evolutionary worldview, morals are not something objective (or absolute); rather, they are a human construct that can be modified or even discarded if desired. Only if there is an Eternal Moral Lawgiver can there exist any type of objective moral standard. The theory of evolution would have us believe that morality sprang from lifeless matter.
Genesis is foundational to the Gospel
The book of Genesis is the foundation for the Gospel. Genesis tells us where we came from, why we are here, what went wrong, and how it can be fixed. We were created by God to worship Him, humanity disobeyed God and brought sin into the world, and God will provide the means of forgiveness for our sinfulness. Genesis provides us with the framework and foundation for understanding everything about our existence. To reject the truthfulness and historicity of the first book of the Bible leaves us without a lens by which to view our universe.
Even atheists realize the foundational importance of Genesis. G. Richard Bozarth, in his article The Meaning of Evolution in the magazine American Atheist, writes:
“Christianity has fought, still fights, and will continue to fight science to the desperate end over evolution, because evolution destroys utterly and finally the very reason Jesus’ earthly life was supposedly made necessary. Destroy Adam and Eve and the original sin, and in the rubble you will find the sorry remains of the Son of God. If Jesus was not the redeemer who died for our sins, and this is what evolution means, then Christianity is nothing.” 
The Genesis record tells us our history, the history of humanity. It tells us why we are here, where we went wrong, and how to be forgiven. Genesis explains our need for a Savior; it explains the reason Jesus died on a cross for us.
The bottom line
The theory of evolution tells us that we are simply a bundle of chemical processes living out our lives on earth with no real purpose except to satisfy our own lusts and desires (whether these be moral or immoral). Secular naturalistic science declares that God does not exist and that this life is all there is. Secular science also says that a man cannot be resurrected. Are we to believe Jesus was not resurrected because secular science says things like that don’t happen? Does this mean we must cater to their ideas in the area of Jesus’ resurrection  too? Will we trust God, and His Word, or the fallible theories of humanity?
“The fear of the Lord is the beginning of wisdom, and the knowledge of the Holy One is understanding” (Proverbs 9:10 NASB see also Psalm 111:10; Proverbs 1:7).
Related reading: How Do Christians Explain Evolution? 
Resources:  Mohler, A. 2010. Why Does the Universe Look So Old? Acts & Facts. 39 (10): 4-7.  Ham, Ken. Genesis: Does it Matter? https://answersingenesis.org/genesis/genesis-does-it-matter/.  G. Richard Bozarth, “The Meaning of Evolution,” American Atheist (September 1979): p. 30.