And the Lord God commanded the man, "You are free to eat from any tree in the garden; but you must not eat from the tree of the knowledge of good and evil, for when you eat of it you will surely die (Gen 2:16-17)."

We humans were created from the beginning to live as the fulfillment of God’s word, which is the will of God, and we are required to listen to him through our spirit and be faithful and obedient to him doing what he says. Instead, to live according to our own thoughts and ideas by not listening to him and not doing what he says is to eat from the tree of the knowledge of good and evil. The former brings life and blessings, and latter death and curses. The same difference is seen in the covenant that the people of Israel had with God—life and blessings if God’s commands are kept, and death and curses if not.

This day I call heaven and earth as witnesses against you that I have set before you life and death, blessings and curses. Now choose life (Deut 30:19).

You need to keep in mind that this choice between life and death is only for those who remain under the covenant with God. It was only in the Garden of Eden that humans had the choice between the two trees. Once they were driven out of the garden, they had no choice but to live under curses. The people of Israel who were brought into the Promised Land had this choice, and we believers under the covenant through Christ have this choice as well: in a spiritual sense, we have been brought back to the Garden of Eden. Speaking of Christians, the Bible says:

Therefore, brothers, we have an obligation—but it is not to the sinful nature, to live according to it. For if you live according to the sinful nature, you will die; but if by the Spirit you put to death the misdeeds of the body, you will live, because those who are led by the Spirit of God are sons of God (Rom 8:12-13).

To walk according to the spirit is life, and to walk according to the flesh is death: this choice, we have now. The former means to live as the fulfillment of the word by accepting it and doing what it says, and the latter means to live with the soul in the center of our being, according to its thoughts and ideas, by ignoring God’s voice that comes through the spirit. With no fulfillment of God’s word, his will and good purpose, it results in spiritual death. In such a condition, it is totally impossible for us to obey God’s commands and do his will. We can still understand mentally in our head that his commands are good, and try to keep them with all our efforts, but we always find ourselves not keeping them. The reason is that the word is not in our hearts. For this very reason, God sent his Son to us.

For God, who said, "Let light shine out of darkness," made his light shine in our hearts to give us the light of the knowledge of the glory of God in the face of Christ (2 Cor 4:4).

Our sin had to be removed in order for the word to come into our hearts. The Bible also says:

The unfolding (lit. entrance) of your words gives light; It gives understanding to the simple (Ps 119:130).

Once the word comes into our hearts, it becomes a part of our own thoughts and desires so that we can do his will as something we want to do with a pure heart without any superficial or legalist attitude—true freedom. This is also explained as follows:

… for it is God who works in you to will and to act according to his good purpose. Do everything without complaining or arguing, (Phil 2:13-14) …