Why did God block the entrance back into the garden after Adam and Eve sinned?
God put man in the garden to tend to it. ‘This was like a park (Gen 2:8) paradise, by which it is rendered in the Septuagint, gives the more precise idea of a spacious enclosure-an extensive park, like those in which Eastern monarchs enclosed their palaces, and which abound with every species of trees, flowers, and garden culture, enlivened besides by numbers of choice animals, which are kept there for pleasure.’ (from Jamieson, Fausset, and Brown Commentary)
Each day in the late afternoon after the day was done a visible presence of glory would appear, this would separate God from the other creatures there.
Gen. 3:8-9 'And they heard the voice of the LORD God walking in the garden in the cool of the day: and Adam and his wife hid themselves from the presence of the LORD God amongst the trees of the garden.”
God had pointed to one tree in the garden to present a test for man and woman. He allowed them the freedom to choose (as was done in heaven by the angels before). God gave a command to Adam and Eve to obey to prevent this from occurring. He was allowed to eat from the tree of life in the midst of the garden but he was not to eat the fruit from the tree of knowledge Gen. 2:17, because when he eats of it he will die. The trees were actual trees, and were emblematic.
If Adam and Eve had passed the test it would have confirmed them in creature holiness, and their offspring would inherit a nature like theirs, of holiness. They then have access to the tree of life and live forever in the garden.
Each day in the late afternoon after the day was done a visible presence of glory would appear, this would separate God from the other creatures. After they sinned (Gen. 3:8) they hid themselves among the trees instead of going out to meet him.
Gen 3:23-24 ‘Then the LORD God said, ‘Behold, the man has become like one of Us, to know good and evil. And now, lest he put out his hand and take also of the tree of life, and eat, and live forever’— therefore the LORD God sent him out of the garden of Eden to till the ground from which he was taken. So He drove out the man; and He placed cherubim at the east of the garden of Eden, and a flaming sword which turned every way, to guard the way to the tree of life.’
The law -- forbidding to eat of the tree was now violated. Adam and Eve were banished from the Garden because they ate from the tree of knowledge of Good and Evil. But it was still possible that Adam might partake of the other tree that he was already eating from. The sentence of death had been passed upon him and eating from the other tree (the tree of life) would bring him in a permanent condition of death. So they were banished from this place that was made in perfect harmony. This was to prevent them from going back in and eating from the tree of life that would affect them to be permanently in this state. If they ate of this tree again it would avert redemption to them and all mankind. This would interfere with the savior who was promised to come (Gen.3:15). Later on the garden was destroyed in the flood.
The prevention back into the Garden was not only an act of justice but of mercy. For them to continue to live in the sight of the tree that made them fall and the one that would give them live would be a constant reminder of their disobedience.There was only one way in to this area God first put man in so he had it guarded by a Cherubim (angels) and glory took the form of a sword that prevented them from entering (this may have meant the garden was a valley in the midst of mountains as there was one way in).
The flaming sword was able to turn every way rapidly, in constant motion, the fire represent divine wrath if they were to disobey and return. (an angel with a sword is also seen with Balaam in Num.22:23)
Later on the Lord had Moses build the tabernacle there was only one way into it, through the tribe of Judah.
Now God has made only way back to have eternal life- through Jesus Christ who is from the tribe of Judah.