In the beginning of the Bible, it tells/shows us in Genesis that the perfection of human life, as walking with God. If we take that symbolism and develop on it, then not to be able to walk with God means death. The same thing that God warns Adam and Eve would happen if they ate of the fruit of the Tree of Knowledge. And in this regard we need to understand the Covenant of Creation where God covenants with Humanity, through the act of creating the Garden that Creation is (7 means sheva meaning covenant), and placing of humanity at the very center of it. There is a relationship here that is proposed and understood. Adam is the high priest of creation, and God will listen to his petitions and intercession on behalf of the rest of creation.
Then comes the Fall, and God does not desert or reject His High Priest, rather promises to restore him back to His office, and to the relationship humanity enjoyed before the fall, i.e. a full life with God, meaning being able to walk with God again. These are wonderfully going to come to fruition in the ministry of Jesus in His death and resurrection, where his burial is in a garden, where He is resurrected in that garden, identified as the Gardener, and then goes on to walk with 2 people, unnamed, because they represent all of humanity and who are standing in for Adam and Eve.
This is the understanding we can take forward, when we read Jesus’ words, “Truly, truly, I say to you, if anyone keeps my word, he will never see death.” Believe.