God would not leave Adam and Eve destitute. The promise God made in this chapter is called the proto-evangel, the first prophecy of the Messiah. Understanding Who the Messiah would be, and what He would do, was going to slowly unfold throughout the Old Testament. Then, throughout the New Testament, Who Jesus is and what He has done is revealed.
Eden was luscious because God had carefully designed and planted it Himself. Now God gave adam, the human being, this exquisite Garden, along with a purpose and responsibility: adam was to continue in the work God had started, cultivating and sustaining the beauty of Eden.