What happened to Adam's nature when he ate the forbidden fruit?
When Adam ate the forbidden fruit, he immediately became a sin-natured individual. His nature changed from being perfect, with not an ounce of sin, to a nature that constantly thought contrary to God's laws, despite himself. Every human being has inherited that sin nature ever since.
Les teaches that Adam was created perfect—not an ounce of sin in him, not a sinful thought—and as pure as Christ in His earthly advent. But as soon as Adam took that step of disobedience in the garden, simply taking and biting the forbidden fruit, he immediately became a sin-natured individual. From then on, in spite of himself, all he could constantly think was contrary to the very laws of his Creator God. Les emphasizes that every human being has inherited that ever since. So people are not sinners because they break the law; they break the law because they are sinners, and they are sinners because they are sons of Adam.