First we may relate them to the two paths Jesus talked about: the path of life and the path of destruction. Eating from the tree of life is similar to choosing the path of life, and eating from the tree of knowledge is similar to choosing the path of destruction. Adam and Eve chose the path of destruction.
Choosing the path of life involves choosing to follow rules and regulations-- of obedience. Adam and Eve had rules to follow, but they chose to break the rules. Disobeying rules is the path of destruction.
"Life" here means more than biological life or the existence of all living beings. It is the fullness of life; it is life at its best. It is meaningful life. The primary condition for such life is holding right relationships. We need to be at right relationship with God, the source of life, with our fellow beings, and with earth, the ground of our existence. The right relationship is a love-relationship. It is being a friend to all.
The Gospels present before us three different Greek words to mean "life"-- bios, psuche, and zoe. Jesus speaks about “…anxieties and riches and pleasure of this Bios.” (Luke 8:14). Jesus says, “For whoever wants to save his Psuche shall lose it.” (Matt. 16:25). Speaking about Jesus, John says, “In Him was Zoe, and the Zoe was the light of men" (John 1:4). These three Greek words probably represent three levels of human existence-- bios at the bottom, psuche at the middle level, and Zoe at the highest level. Jesus asks to choose the path of zoe as opposed to the path of destruction.
The tree of life at the center of the garden represents life at its best, in its fullness. It seems that Psalm 1 sings about this tree.
Happy are those who do not follow the advice of the wicked,or take the path that sinners tread,or sit in the seat of scoffers;but their delight is in the law of the Lord,and on his law they meditate day and night.They are like trees planted by streams of water,which yield their fruit in its season,and their leaves do not wither.In all that they do, they prosper.
It is a life supported by right relationships. Once the relationships are broken, life at its fullness cannot be sustained, and death happens. To refer to the tree of life, the Greek word used in the Book of Revelation is Zoe, the highest level of existence.
When Adam and Eve broke their relationships, they lost their life in this sense as well. They died in this sense. That is why God said, "You shall die the day you eat of this tree!". They disobeyed, and the relationships were broken, and they died.
The word "death" is used here metaphorically. It is not the real death that all beings die. This is something like death. When relationships break, life at its fullness ceases to exist, and this condition is very much like death. When a love-relationship breaks, it causes a lot of pain. This pain is similar to the pain when someone close to us dies. That might be one of the reasons for relating the break of love to death.
Paul relates Jesus to Adam, and calls him the second Adam. Adam disobeyed and brought death, but the second Adam obeyed and brought life. The first Adam chose the path of destruction but the second Adam chose the path of life. Paul exhorts all people to follow the lead of Jesus and choose the path of life.
John's Gospel speaks about life and eternal life. Here too the word refers to the fullness of life. Jesus invites people for a new birth, which effects a transformation in human life like water becoming wine. Jesus is presented as the way to eternal life.
On Good Friday we sing, "The Blessed One by his death killed death." It makes a distinction between the death that Jesus died and the death that he killed. The death he died is the normal death that all living beings die. God is the only deathless being. But the death that Jesus killed is the same death the Adam and Eve died on the day they ate the forbidden fruit. Jesus killed the death of the broken love-relationship, which means that he reestablished a love-relationship.
Malayalam, my native language, has two different words for life-- jeevan and jeevitham. It is the presence of jeevan, the life-energy, that distinguishes a living being from a nonliving being. All living beings have a jeevitham, that lasts for a duration of time. Although the same jeevan animates all living beings, we can build up jeevitham of different quality, such as Bios, Psuche, or Zoe. It seems to me that the word life in most of the places in the Bible refers to jeevitham. If so, the path of life will be jeeevitha maargam, and the tree of life will be jeevitha vriksham.
One final question: Why is the forbidden fruit called the fruit of the tree of the knowledge of good and evil? Isn't knowledge desirable? In what sense is knowledge related to the path of destruction?
There is a fine distinction between seeking wisdom and claiming to be wise. They are opposite to each other like light and darkness. In ancient Greece, there were sophists (those who claimed to be wise) and philosophers (those who called themselves lovers of wisdom). Once you claim to be wise, you close your mind, and no new information can enter your mind. As long as you seek wisdom or call yourself a lover of wisdom, your mind remains open.
The knowledge of good and evil is ultimate knowledge that belongs to God. No human being can claim to have such knowledge. Today, as always, most of the religions and ideologies claim to have the ultimate knowledge of existence in their custody-- they eat from the tree of knowledge. The greatest threat to peace in our world is from those who claim to have ultimate knowledge. Such people, who claim to have the custody of ultimate knowledge, always clash with one another. They don't admit that God alone has ultimate knowledge. They don't care for maintaining the love-relationship with God, with fellow beings, and with the rest of the creation. Thus they choose death rather than life.
In conclusion, in order to have a full life, we need to have an open mind, willing to learn always and from everywhere. We also need to learn to follow rules and regulations. Also we need to build up and maintain all of our relationships intact. In short, learn, obey, and love.