In Adam and Eve's time, the serpent deceived them to take the fruit from the tree of knowledge of good and evil. As they take the fruit, they will “become like God, knowing good and evil.” The enemy's goal was to dismiss humanity's dependence on God . They would make self judgments on matters without consulting God.
Today, the enemy's deception upon humanity is still strong and prevailing. Many depend of self and dismiss the fact of their need for God. So the question pops, “Why do we need God?” Simply put, we are not all self-sufficient.
We live, move, breathe and exist because there is a Creator who fearfully and wonderfully made you and me. The essential existence of our will to live comes from God - which explains the reverse: the essential existence of the will to no longer live (suicide, depression, etc) comes from the evil one.
We live hoping for a better tomorrow, a better life, a turn of fate into a positive one. Where does this hope come from? It may come from the desire to be better than our surroundings, or the need for survival. We may attribute this hope we have to ourselves initially, but it will soon die as meaninglessness and hopelessness creep in from happenings around.
So back to the question: Why do we need God? Because
1) He is our Creator. Without Him, we would not be here today.
2) He brings us to hope anew - in the midst of good and trying circumstances.
3) He is our Provider. He is the sustenance of all lives, and He promises we will always have enough - if we will trust Him and seek first His Kingdom.