There are many ways to answer this question. Let me mention just two for now, even as they are both related to one another.
First, it may surprise some of us to consider that the Bible will often speak of the human longing for "freedom" as something only God can ultimately and irrevocably satisfy. Again, this might seem strange to us since it is often the case that we think of religion and even God as the source of bondage and the root cause of oppression and abuse of power in the world. And to be sure, some religion has been used as a coercive force in the world for personal and/or political gain. Likewise, it is often the case that religion, especially if we grew up in a context where religion was all about rules, is then associated with taking the romance and life out of living! And to be sure, some religion, especially with an emphasis on "don'ts" gives this impression. And so, you ask, how can we speak of our need for God as related to our need for freedom? Fair enough!
It can be observed that the story of God's people throughout the Old and NewTestaments is described in terms of God giving his people "freedom." Words like "deliver, redeem, set free"-- all words of freedom- are throughout the Biblical history descriptive of what God can and does do for humanity. Sometimes, this is related to God setting people free from oppressive people and regimes. Other times, and perhaps most especially, it is setting us free from oppressive forces or impulses from within ourselves that hold us into bondage such as to rob us of real human flourishing. Listen, for instance, to how the apostle Paul describes life with God as a Christian: "for freedom, Christ has set us free" (Gal.4:31). And elsewhere in the Bible, all of creation is described as yearning to be "set free from its bondage" in relation to the work of Christ wherein all of creation is said to "obtain the freedom of the glory of the children of God." (Rom.8:21).
The point that I am making here is that we all serve something in life. We all serve "gods" in so far as what we serve promises us, even if in our own minds, life in some sense. And so the question is whether or not what we serve is setting us free to live life in the fullest as consistent with who we are and the nature of the world, or are the things we serve putting us in bondage such as to deprive us of real human flourishing. Perhaps another way to explain this is to say that we are really never absolutely free. Our freedom is always a relative freedom -- relative to serving something that serves our human flourishing, or something that doesn't. Freedom, whenever it is spoken of, is always relative to something we are set free from in order to be free to. And so the question is this -- are we serving that which can deliver what we really need to flourish, or is it something that saps life from us? When we want "freedom," isn't it that we are really wanting to give ourselves to something that is life giving and life fulfilling?
It is therefore perhaps a great irony to some of us that the very word "sin" that we often associate with "freedom" and "fun" is used to describe something that enslaves us throughout the Bible! (Rom. 6:20). That is to say that our lives can never be a life of no service (of no "gods"), rather our lives are always lived serving something. And if it promises us "life," however we define it, then it is our "god(s) in a sense. " And so the question is this, can what we ultimately serve deliver real and abundant life? If it can't, it is oppressive, promising life, if but in our own minds, but unable to deliver it in any full and deep sense.
And so one reason we need God is to be free -- free from the fear of others opinions of us if we serve other people or social prestige, free from the fear of failure if we serve our jobs, free from the fear of condemnation if we serve morals or religious devotion even. And not only do we need God to set us free FROM the things that oppress us, we need God to set us free TO the fullest experience and participation of those things that God has given us to enjoy! To be sure, it would be for another time, to talk about all the "do's" in the Bible -- sex and romance, wine, vocation, deep and meaningful relationships, the arts, nature -- the list could go on and on as to the "do's" that pertain to all of these things and more, and always with a basic caveat, "do it better with God than without! If our understanding or experience of religion is that God is a despiser of real living-then we have not the experience that is over and over again described in the Old and New Testament with God!
A second way to answer the question of why we need God is related to our own identity and wholeness. For according to the Christian way of thinking, the most fundamental essence of our nature is that we are made in "the image of God"(Gen.1:16ff). To say it differently, we are not merely the sum total of our biological parts, we are in the words of Genesis "a living soul" (Gen.2:7) even that God's spirit is described as "abiding" in us (Ge.6:3). This is to say that while we are not ourselves gods, we are made to partake of God. Inversely, life without God is life devoid of God's Spirit, which then is to live in the absence of the fullness of life, since God is "life and life eternal." And so another reason we need God is to be most fully human by partaking of God's nature even. And so there is this amazing verse in the Bible-- one that describes what I am talking about here, especially as this is related to the mission of Christ. It is found in 2 Peter 1:4, where the apostle Peter describes life with God "that we may become partakers of the divine nature."
I suspect that much of the deep dissatisfaction and discontentment with life that people often feel is related to an identity problem, especially as related to our fullest identity being made to partake of the divine nature. Jesus once said it that his purpose was "to give you life, and life more abundantly." But interestingly, the way to this "more abundant life" is not by receiving something that Christ can give outside of himself, it is by our union with Christ, depicted by Christ as being engrafted into him, even as he is engrafted into God (c.f. John 6:56 and 15:4). Christ then, is described as inviting us to share in his nature, even as he shares in the nature of God, albeit without us becoming "gods' per say, in that both in the person of Christ, as in our being engrafted to Christ by faith, the human and divine natures are kept distinct. There is a mystery here to be sure, but it is a mystery that I think the human soul is longing to experience. I'm reminded at this point of something that another ancient person once noted observed within himself, even as I think it is incredibly relevant for today. For St. Augustine once confessed "My heart is restless until I find my rest in Thee."
And so have you ever noticed how the more we have, the more we need to have, the more we are loved, the more we need to be loved, the more we achieve, the greater our achievements need to be, etc.? Can you remember what happened not long after you acquired something new? Life is like that, isn't it? It's never enough. Figuratively speaking, it is like my sense of "taste" -- the older I get, the more spice I need on my food because nothing "tastes" strong enough any more, and it seems to be getting worse the longer I live.
It is just as the wise teacher in the Bible once acknowledged, "The eye is not satisfied with seeing, or the ear filled with hearing" (Eccle.1:8). The wise teacher was King Solomon, perhaps the most successful person encountered in the Old Testament narrative. It was King Solomon who was renown for his great wisdom "surpassing all who were around" him but who discovered that "this too is vanity." He even compared the search for enough wisdom to an ever-elusive chasing "after the wind." It was also King Solomon, after "making a life long test of pleasure," who once confessed, "What use is it?" And after making for himself the greatest "gardens and parks" and taking possession of great "herds and flocks" and gathering for himself "silver and gold and the treasure of kings and of provinces," Solomon admitted, "All that my hands have done and the toil spent in doing it ... all is vanity and chasing after the wind ...there is nothing really to be gained under the sun" (Eccel. 1:16, 2:1-8).
Life without God is never enough! Why? The Christian answer is grounded in something fundamental about ourselves- that we are made in God's image, and are never complete until we are completed by our union with God. As the Bible affirms, "God himself gives to all mortals life and breath and all things ... in him we live and move and have our being" (Acts 17:24,28). Perhaps nothing more validates the Bible than the fact of our restless human spirit! How much wealth would be enough? How much prestige? How much knowledge? How many trips to exotic places? How much romantic passion? Can any of these things ever be enough to satisfy the deep sense of incompleteness that is within us?
We need God because without Him, we will never be satisfied. We are incomplete without union with God. It is as if there is a God-shaped vacuum in every one of us, only to be filled by the life of God in us! We can learn this lesson sooner, or spend the rest of our lives learning it in frustration later -- what makes better sense to you? I can even now remember the testimony of a man who I knew growing up to be one of the most wealthy and successful men in Atlanta. The title of his address was "Take the short cut." He described a life of wanting it all, and getting it(!), and the utter despair at waking up one morning to the harsh reality that all of his goals had been accomplished and he was still incomplete and "empty" inside. What would be worse, struggling to reach our goals in the hope of finding an abundant life, or actually accomplishing all of our goals and even more than we could have ever dreamed o faccomplishing, and discovering that it is still not enough? The man was on the brink of suicide when he discovered the truth of Augustine's discovery, that "my heart is restless until I find my rest in Thee" (St. Augustine). Thankfully, he tried one more thing. He sought after God!
Dear God, if it is true that I need you in order to really find "rest" for my restless soul, would you open to me the reality of the life of God in me? Would you show me this life, and how I might take hold of it? Would you give me the eyes to see and the ears to hear what no person can see or hear apart from your spirit working in me? And if Jesus is the way to this union with you, give me Jesus!