One of the most difficult doctrines for people, even professing Christians, to accept is that teaching known as original sin. Let me first define it, then demonstrate with three God-given illustrations how clearly original sin is revealed to us.
The term "original sin" does not refer to the first sin of Adam, though it is related to it. Rather, by original sin it is meant that the impact of Adam's sin on the whole human race is that every person comes into this world as a sinner.
Worldly philosophies or Pelagian theologies teach that people are born innocent or morally neutral only to be later corrupted by society. However, Reformed theology upholds that every person is born a sinner (save one - see below). Indeed, every person is conceived in sin, just as David said, "Behold, I was brought forth in iniquity, and in sin did my mother conceive me" (Ps. 51:5). David, confessing his adultery in this psalm, is not saying his mother's act in him being conceived was sinful. Rather, at the moment beginning his existence, his parents' corruption meant he was corrupted as well. He not only confesses his sin in this psalm, but that he was conceived and born a sinner. As J.I. Packer states, "The assertion of original sin makes the point that we are not sinners because we sin, but rather we sin because we are sinners, born with a nature enslaved to sin."
Romans 5 speaks of original sin when the Apostle Paul writes, "Therefore, just as sin came into the world through one man, and death through sin, and so death spread to all men because all sinned" (Rom. 5:12). He says very bluntly in this same passage "one trespass led to condemnation for all men" (Rom. 5:18). The Westminster Shorter Catechism gives a confirming statement of this teaching.
Q. 18. Wherein consists the sinfulness of that estate whereinto man fell?
A. The sinfulness of that estate whereinto man fell, consists in
the guilt of Adam’s first sin, the want of original righteousness, and
the corruption of his whole nature, which is commonly called original sin; together with all actual transgressions which proceed from it.
Sin, entering the whole human race through Adam's fall, now issues forth from all of us, like lava from a volcano, because of our corrupt human nature.
So having defined original sin, how do we see God illustrate it in ways that we experience its truth? Here are three important illustrations to remember.
Babies do not have to be taught to misbehave. To every parent, it becomes pretty clear that not all is right with their cute little baby. As adorable as the infant may be, sooner or later - usually sooner - the child's self-centered nature becomes obvious to all willing to admit it. Every baby, as it grows and is able to express itself more and more, fusses, gets jealous of others, pitches fits, thinks the world revolves around him or her, etc. No one taught the baby to do this. It just comes from its nature. Babies come not only wrapped in pudge, but wrapped up in original sin.
Sin affects people not only individually, but covenantally. When someone sins, like King David did as mentioned above who committed adultery with Bathsheba, that sin always impacts far more people than just the person or persons directly involved. David and Bathsheba's sexual fling was not just a private matter between two consenting adults. No, a nation's war plans took a different turn, a betrayed husband was murdered, a conceived child died, and trouble ensued in David's household for years, culminating in a civil war started by his own son, as a result.
We see the awful, bomb-like impact of sin all the time. A speeding motorist crashes, hurting others and tying in knots commuting traffic for hours. An angry, abusive father brings pain and shame on on his wife and children. A pastor commits infidelity and the church splits apart. A tyrannical leader like Kim Jong-un of North Korea keeps the people under him in abject poverty. All these pictures help us see then that it is not far fetched to believe that Adam, as the first human being, sinned and impacted all that follow him. We see this reality of sin confirmed regularly in human experience.
Jesus' conception then had to be different to break the bonds of original sin. For God's Son to become man in order to save us from our sin, he had to be fully human but he could not be conceived in the ordinary way. Otherwise, he would have carried forward original sin. Thus, we should marvel over the virgin birth not simply because of its miraculous nature, but for the fact that Mary's child was conceived by the Holy Spirit, guaranteeing that "the child to be born will be called holy - the Son of God" (Luke 1:35).
Again, the Shorter Catechism testifies to the truth that Jesus was free from original sin when it states:
Q. 22. How did Christ, being the Son of God, become man?
A. Christ, the Son of God, became man, by taking to himself a true body and a reasonable soul, being conceived by the power of the Holy Ghost in the womb of the virgin Mary, and born of her, yet without sin.
Now illustrated, think of the implications of denying this doctrine. Not only do those who object to original sin deny an explicit teaching of Scripture and observable human experience, but they also deny the necessity of Christ's virgin birth and our great need for a truly holy Savior. Thus, a denial of this doctrine not only leads one to an improper understanding of human nature, but also of Christ's human nature. Trying to hold on to some innate goodness or ability in man means necessarily taking away from the glory of God in Jesus Christ. That's too great a price to pay.