When Adam and Eve sinned, God exiled them from the garden, and through them, sin entered the world. Christ came to redeem sinners and make them into saints. But if Adam had not sinned, then would Christ have come? Could Adam have not sinned?
Here are some Augustinian considerations.
Adam Had Free Will
Adam had genuine free choice, and so he was able to good or evil, sin or not sin. We know this because God says to Adam, “but of the tree of the knowledge of good and evil you shall not eat” (Gen 2:17). Why warn Adam if Adam had no free choice? In fact, the story tells us that for a while Adam did not eat from the tree. So he chose good. Then at a later time, he ate from the tree. So he then chose evil.
Augustine in his work Rebuke and Grace explains that Adam had a first grace from God, a grace that gave him the ability to choose good or abandon it. Adam also did not suffer from the weakness of nature that sin brought into the world. He did have the draw of desire (concupiscence). Romans 7 describes this turmoil of soul. Adam, explains Augustine, had perfect peace.
So Adam had grace that gave him the ability to do good without the weakness of sinful human nature. Yet he still sinned.
Adam’s Free Will Eventually Could and Did Lead to Choosing Evil
The first and powerful grace given to Adam meant he had the ability to do good or evil. But such an enabling freedom means that over an unlimited span of time one may eventually choose evil, especially since death did not impede Adam in this state: “in the day that you eat of it you shall surely die” (Gen 2:17). If Adam did not eat (i.e. remain without sin), then he would live forever. As Genesis 3:22 says, Adam and Eve were exiled from the garden lest they “live forever” (Gen 3:22).
It seems to me that free choice, over a long period of time, means that one will eventually choose evil. In fact, we might know this because the angels had already made their free choice. Some fell with Satan, losing the grace-given ability to choose good; others remained in heaven, and so gained the second grace of being unable to sin. The holy angels remain holy still; the evil angels remain evil still.
This is because the punishment for choosing evil, as Augustine also argues, is the loss of grace. The freedom to only do evil, as the devils have, is itself the punishment they merited by their free choice to fall into evil. “He who is unjust, let him be unjust still” (Rev 22:11). Of course, they continue to merit punishment since their sin merits judgment.
Adam Lived Apart from First Grace
Since God is the source of goodness and the goal of the good life, living outside the grace of God is like living without water. We are meant for water. It enables us to live. But the loss of original grace and the gaining of inheritable evil meant that human freedom lost its ability to choose good. As Augustine says, free will is sufficient for evil, not for good, unless God’s omnipotent power helps us.
When God exiled Adam and Eve from the garden, they lost access to the tree of life through which they would live forever; and they apparently lost the ability to not choose sin, since life outside of the garden is marked by sin (Gen 4) and death (Gen 5), the very things avoided by doing good (Gen 2:17).
Human life is marked by deep internal conflict (Rom 7). And so even if we had the first grace Adam had, then we’d still be enticed by desire for evil. So we need a greater grace.
A Greater Grace in the Second Adam
Augustine makes the fascinating argument that when God assumed humanity that this act shows how God will save sinners. At the moment of Christ’s birth, he was not only able to choose good but also had the will to choose good. Meaning, Christ always chose willingly to do good.
In our salvation, we gain not only the ability to freely choose good but also the will to truly conquer sin and concupiscence. Now, that ability and will come to perfection at the resurrection. Even if this argument does not compel us, whatever else happens in salvation, Christians not only can choose the good but the Holy Spirit moves their will to want it.
So this second grace is more powerful than Adam’s grace, since Adam did not have a fallen nature but an unfallen one.
Could Adam not Have Sinned?
Adam’s free will meant that he could choose evil. And without a second and greater grace to always will the good by the Spirit’s union to the flesh of Christ through which we receive all that Christ is.
That means we not only can do good but we want to do good because the Spirit of God inhabits us. Before, as created effects (creatures) of the Creator, we could imitate God accordingly. But now that God’s Spirit indwells us and communicates to us the benefits of Christ’s glorified flesh to us, we will what God wants, the good, the best.
Whatever the precise answer might be, Adam did sin because he did not perfectly will the good. Christ could choose the good and was unable to sin. We can choose the good, and are able to not sin too, although the perfection of this second grace occurs in the resurrection.