In the story of the flood, we have the spread of evil to all human society. Here is how the biblical writers put it.
The Lord saw that the wickedness of humankind was great in the earth, and that every inclination of the thoughts of their hearts was only evil continually. (Genesis 6:5)
Now the earth was corrupt in God's sight, and the earth was filled with violence. And God saw that the earth was corrupt; for all flesh had corrupted its ways upon the earth. (Genesis 6:11-12)
And when the Lord smelled the pleasing odor, the Lord said in his heart, "I will never again curse the ground because of humankind, for the inclination of the human heart is evil from youth." (Genesis 8:21a)
Here is the explanation in the course materials.
It would be impossible, after this development of the theme of sin, to think of it only in terms of "bad things" that people do. Sin is not simply a few bad actions which occur more or less on the surface of life, so that we might go through a whole day, perhaps even longer, having "committed" no sin. Pride, community alienation, and corruption of the heart are, in the point of view of the biblical writers, more than part of the everyday makeup of humankind; by our fallenness they have become part of us. If we do "right"--and the biblical writers are as insistent on our obligation to do so as they are on the fact of sin--it will be through obedience, and not by "doing what comes naturally." The "nature" of humankind, in the true sense of the word, is "good" because we are God's creatures and are in God's image; but what has become "second nature" to us is not to be trusted: the "thoughts of the heart" are "only evil continually"! (Pages 92-93)
That last sentence in the course materials is important: "The 'nature' of humankind, in the true sense of the word, is 'good' because we are God's creatures and are in God's image; but what has become 'second nature' to us is not to be trusted: the 'thoughts of the heart' are 'only evil continually'!"
Is it true that the thoughts of our hearts are only evil continually and that our second nature is not to be trusted? I wouldn't put it like that. I certainly don't think that it's helpful to teach this to children. Here's why: This implies that the source of our evil is inside us and that the source of our good is outside us. The course materials even say that the way we do good is through obedience, not by following what comes naturally to us. Obedience implies an outside authority whom we obey.
My goodness! Think how grumpy that will make / does make us. I have all these things I want to do naturally, but they aren't good, they are sinful, so to be good, I have to obey what God says even though I don't naturally want to. I spend my life suppressing what I naturally want and obeying this outer authority. I never get to fulfill my desires because I always have to obey God's desires. I'm always going against the grain.
I can think of an acquaintance who did something like this in real life--he obeyed his father rather than what he naturally wanted to do. This acquaintance naturally wanted to make music. He wanted to major in music in college and become a musician. His father, however, wanted him to be a partner in the family business and insisted that his son major in business and then work in the family business. This acquaintance did so. He did not follow what he naturally wanted to do (become a musician) but chose to obey his father (become a partner in the family business). This made him very unhappy and ruined his marriage. The minute his father died, he sold the family business and returned to his first love, music. And he is much, much happier!
The story of this acquaintance is much like what I experienced when Jesus was on the throne of my heart, controlling my life. I couldn't do what came naturally to me because I had to obey what Jesus wanted me to do. I was unhappy and grumpy because I was trying to twist myself into someone I wasn't, just as this acquaintance was doing. As soon as I removed Jesus from the throne of my heart and put myself back in control, I was much happier.
We just aren't going to be happy by suppressing who we are and what we desire in order to obey commands coming to us from outside ourselves, from God.
And it's just plain old not true that the thoughts of our hearts are only evil continually. Good is inside us. It's part of who we are as human beings. We need to learn to look, not to commands from God outside ourselves, but to our inner depths to discover what we desire at our core. We desire good. At our core, we will find a God-place that is ALREADY THERE INSIDE US AS PART OF OUR BEING. This is a place filled with wisdom, compassion, justice, creativity, love, joy, peace. It is far different from the surface emotions that blow across our lives and that can lead to evil, as when we hurt someone in anger just for the momentary rush of power or take from others to alleviate our fear of not having enough.
I believe that it is wrong to say that acting on surface emotions is acting from our selves and that acting from the deep God-place is acting in obedience to God outside ourselves, as though the evil comes from us and the good from an outer God. No, the evil and the good are both part of us--the evil on the surface and the good at our deep core. The deep core is very accessible. I found this out quickly once I got Jesus off the throne of my heart and looked to see what I really deeply want. What I really deeply want is not to get a momentary rush of power by displaying anger or to frantically alleviate fear by seizing what I think I need. What I really deeply want is to act from wisdom, compassion, justice, love. This is what I myself want, not just what obedience to God's commands asks of me. When I am just obeying God, I become grumpy because I am suppressing what I want. But when I myself find and act from the goodness within, then I am joyful.