Evolution does undermine Christianity.
Exodus 20:11 says that in six days God made the heavens, the earth, the sea and all that is in them, and on the seventh day He rested, therefore they were to keep the Sabbath day holy. Therefore, it's impossible to put millions of years in
Genesis 1.
God created everything, not random chance over millions of years of death.
The foundation of the gospel is from
Genesis 1-3 - rip it out, and you are left with nothing.
God's creation was very good (
Genesis 1:31), and death had no part in it. Originally man and animals were vegetarians (see
Genesis 1:29-30). Death is what God told Adam would happen if he ate the fruit God commanded him not to eat (
Genesis 2:17). Adam ate, and death came to all men, both spiritual death and physical death (
Romans 5:12).
But God did two remarkable things on that sad day. Number one, He promised a Savior from the Seed of the woman (who we know now as Jesus) (
Genesis 3:15). Number two, He instituted the first blood sacrifice for sin (
Genesis 3:21). It doesn't say what animals died, but animals don't give up their skins without being killed. God used the skins to make clothes for Adam and Eve, to cover their shame and nakedness. Recall that they made fig leaf coverings themselves, but they still hid from the presence of God (
Genesis 3:7-10). Only the sacrifice God provides can cover the shame of our sin - not our own human effort (
Romans 3:20). Through the rest of the Old Testament, God drove home the point that the shedding of blood was required to pray for sin (
Leviticus 17:11,
Hebrews 9:22). This is because the life of a creature is in the blood (shedding blood - causing its death). God Himself said death would be the penalty for sin before it happened (
Genesis 2:17,
Romans 6:23a).
So, why is it significant to the gospel? Because in order to satisfy the justice of God, there has to be a blood sacrifice to pay for sin. God can't just forgive. Since the blood of bulls and goats can't take away human sin (
Hebrews 10:4), we needed a perfect man to die in our place. But all men descend from Adam and inherit a sin nature. The only way God could offer us grace and forgiveness was by Himself being clothed in flesh and becoming a sinless sacrifice. Jesus' death on the cross and all that led to it was unimaginably brutal. Jesus wouldn't have done it if there was any other way for men to be forgiven. He asked His father to let this cup pass from Him, if it were possible. I still don't understand why He loves us so much.
The main reasons people believe in millions of years is because of the fossil record, which is full of death (even sickness and animals eating other animals). It's supposed to represent the time before man evolved. However, the Bible says the entire world was flooded, so that gives us a good idea of how many of the fossils and rock layers came into place. Further, since God says death is the penalty for sin, there shouldn't have been death prior to man. Some people say, "Well, man didn't die prior to Adam's sin, but that doesn't preclude animals from dying for millions of years." God wouldn't have called His creation "very good." People don't realize the curse affected everything in creation - not just the serpent's legs, the woman's childbearing, the thorns and death to mankind (
Romans 8:20-22). For example, man (
Genesis 9:3) and some animals are carnivorous. Animals (many) are afraid of man (
Genesis 9:2). When Jesus comes back and reigns on the earth for a thousand years, the animals will return to their Edenic diets and dispositions (see
Isaiah 11 and
Isaiah 65). Since this is part of the removal of the curse, it also follows that it was not part of creation prior to the curse. Death is an enemy, not a means of creating.
I hope this helps you. God bless.