But of the tree of the knowledge of good and evil, you shall not eat of it: for in the day that you eat thereof you shall surely die.   - Gen 2:17

Since all Humans are born in Sin with a dead spirit (SinNatue) they cannot grasp what life as a Spirit Being is like.   

So, they live Carnal lives driven by the Lust of the Flesh.   

God is a Spirit (Joh 4:24).    Man cannot truly connect with God except by the Spirit.   So, God has born us of His Spirit ( New Birth).   

We still have an unregenerated Soul and a Body that is tuned to serve itself.   

The Mosaic Law could not make a man Righteous.   Keeping it could not enable a man to Fellowship with God.   That Law served only to teach men somewhat about the nature of God and to keep him from destroying himself.   

Jesus said that a person cannot see the Kingdom Of God much less enter the Kingdom Of God except by being Born Again.   

Why?   Because the Kingdom Of God is in the Spirit Realm.   It is where God manifests His Glory.   

Yes, the Universe and Earth along with plant and animal life manifest part of the Glory of God but they are only types and shadows of the real Glory that is found in His Presence.   

Adam and Eve walked with God (Gen 3:8).    They Fellowshiped with Him until Sin caused them to fall our of the Spirit Realm.   

Jesus came to restore Humanity to the place which God intended all along - in Fellowship in His Presence.   

You must see yourself as a Spirit Being with a Soul and a Body keeping the chain of Authority in correct priority - Spirit controls Soul which controls Body.   

When we do so we will have the Mind Of Christ who, though He has a Soul and Body, lived and walked in the Spirit Realm by Faith (Joh 3:13) .   

Jesus was and is a Spirit Being and He is the firstfruit (1Co 15:23) of many such Spirit Beings of which I trust that you are one!   

This was accomplished by Forgiveness Of Sins (Col 1:14) that enabled Regeneration (Tit 3:5) through the perfect Work of Christ Jesus.   

We are instructed to Walk In The Spirit because we Live In The Spirit (Gal 5:25).    Simply put this means that we now Walk with God in the Spirit Realm just as Adam did before He sinned and his spirit died.