The genuine good is God Himself (Matt. 19:17a); hence, gaining God equals gaining the genuine good. When the rich young ruler came to the Lord Jesus and called Him, "Good Teacher," the Lord Jesus said, "Why do you call Me good? No one is good except One—God" (Mark 10:17-18). If besides God we gain any other good, that is terrible. If we touch the good things outside of God, this means that we touch Satan. The Bible teaches us that knowledge, good, and evil all are Satan. In the tree of the knowledge of good and evil, therefore, evil and good are equal.
The two trees are not for producing materials but for man to eat their fruit (Gen. 3:3, 6b), the fruit of the tree of life becoming food to man for nourishing, for the dispensing of life, and the fruit of the tree of the knowledge of good and evil becoming poison to man for killing. To eat means to take in something that is outside of us and then digest and assimilate it. We must be careful concerning what we eat. Surely, today's television and so many different kinds of newspapers and magazines are branches of the tree of the knowledge of good and evil.
The two trees are two sources.
The two trees, as signs of God and Satan, are the two sources of two categories of men. The first tree is the source of men who seek God as life for their supply and enjoyment, of whom Abel is the leading one (Gen. 4:4). The second tree is the source of men who follow Satan as their poison unto death and eternal perdition, of whom Cain is the leading one (v. 5).
The outcome of the two sources becomes two kingdoms on the earth. The first is the kingdom of God, which was first the kingdom of Israel according to God's Old Testament economy and then the church according to God's New Testament economy (Matt. 21:43). The second is the kingdom of Satan (cf. Matt. 12:26; Col. 1:13).