Why does it matter if we kill someone?
The secular view, that we are products of chance or "lucky animals", is terribly inconsistent with human beings having inherent value. In direct opposition, the Bible teaches that we are made in the image of God. This means ever human being has value, regardless of their mental, physical, or social state. Therefore it matters if we kill someone because we're ending the life of something made after God's likeness. God says in Genesis 9:5-7 that He will require our life as payment if we kill someone unjustly. 

To kill or not to kill? Is it ever justifiable for the government to kill? Sometimes (Romans 13:1-4). What about a soldier or police officer? Sometimes (Romans 13:1-4; Luke 3:14). Is it ever justifiable to kill in self-defense? Sometimes (Exodus 22:22-23). What about abortion? Although some of the before mentioned issues have grey areas, it seems abortion does not. Biblically, scientifically, and rationally, abortion is murder. We're not meant to murder, we're meant to love—love God and love those made in His image. Those who have murdered have blood on their hands, and what they are owed is death. However, the bloodguilt on the hands of every murderer is, I dare say, on all of us. Jesus clarifies in Matthew 5:21-22 that if we are even angry at or insult our brother that we are liable to the same judgement. 

How can we do what we should—love? First, in order to love like we should, we need to have our bloodguilt removed. Thankfully "in [Jesus] we have redemption through His blood" (Ephesians 1:7). We owe our blood to God yet the gospel says that on the cross Jesus stepped in and spilled His in our place. Second, in order to do what we should, we need to have a deep, life-changing motivation to love. You’re only going to love like you should to the degree that the bloodguilt-freeing, self-sacrificial, unmerited-love of Jesus is your treasure and focus. Murder says, "your life for mine." Jesus says, "My life for yours." Is He your treasure and focus? If so, you are forgiven and will begin to love God and others like you should.