If anyone is able to receive it, the tree of life is guarded by a cheribum with a flaming sword.
Three things could be symbolized here.
1.) The cheribum signifies the glory of God.
2.) The flame of the sword represents the holiness of God.
3.) The sword represents the righteousness of God.
God now has a three-fold requirement upon the fallen man that keeps him away from eternal life.
The sinner is short of the glory of God.
The sinner falls short of the holiness of God.
The sinner is condemned by the righteousness of God.
These three demands cause a barrier separating man from the fulfillment of God's eternal purpose in creating man. The requirements must be met in the Son of God on our behalf latter in the New Testament.