The science of embryology establishes that from the earliest stages of development, the unborn are distinct, living, and whole human beings. Breaking that down, the embryo is:
Distinct from the mother -- with his or her unique DNA and possibly different blood type, for example
Living -- continuing to grow and develop at a rapid pace
Whole -- everything needed for development is already present
While the early embryo does not look like an adult, it does look exactly as a developing human should at that stage of development. "Embryo" and "fetus" are simply stages of life in a span that includes others -- such as "infant," "toddler," "adolescent," and "adult."
Scripture teaches that all humans have value because they bear the image of their Maker (Genesis 1:26-28, James 3:9). Because humans bear the image of God, the shedding of innocent blood is strictly forbidden (Exodus 23:7, Proverbs 6:16-19, Matthew 5:21). We are never to kill innocent human beings.
Abortion is the intentional killing of an innocent human being. The same passages in Scripture that forbid the shedding of innocent blood apply to the unborn as they do to every other human being.