1. Genesis 2:17
    but of the tree of the knowledge of good and evil you shall not eat, for in the day that you eat of it you shall surely die.
  2. Genesis 3:1
    [ The Temptation and Fall of Man ] Now the serpent was more cunning than any beast of the field which the LORD God had made. And he said to the woman, “Has God indeed said, ‘You shall not eat of every tree of the garden’?”
  3. Genesis 3:5
    For God knows that in the day you eat of it your eyes will be opened, and you will be like God, knowing good and evil.”

  4. What does "eat of" mean? Is there any difference in meaning between "eat of" and "eat"?
Its an archaic way of speaking. Eat it, eat from it, eat part of it.
sitifanIs there any difference in meaning between "eat of" and "eat"?
There is more difference in style than in meaning, although the meaning is slightly different. The Bible is written in very old English, including very archaic "partitive" structures using "of".

eat of it ~ eat some/any of it ~ eat some/any part of it.

It's not exactly the same as "eat it". That would imply "all of it".

The partitive is not used in modern English except in imitation of archaic religious style.

Here are others:

Then the Lord said to Adam, You shall not now take of it, for it has been assigned to the cherubim and the flaming sword ...
And it came to pass that when he said these words, he commanded his disciples that they should take of the wine of the cup and drink of it ...
Eve was tempted by the lying words of the Snake and desired to taste of the forbidden fruit but she was afraid to taste of it
alone ...