Humans need God. If that were not the case, we would not have been told to spread the Gospel to the ends of the earth -- the "Great Commission:"
* And Jesus came and spake to them saying, All power is given unto Me in heaven and in earth. Go ye therefore, and teach all nations, baptizing them in the name of the Father, and of the Son, and of the Holy Ghost; teaching them to observe all things whatsoever I have commanded you: and, lo, I am with you always, even to the end of the world. Matt. 28:18-20.
But why did we have such a commission?
It was part of the plan from the very beginning. The promise to Abraham was that all the nations of the world would be blessed through him:
And in thy seed shall all the nations of the earth be blessed; because thou hast obeyed my voice. Genesis 22:18
God is a blessing, and God coming to earth as a Hebrew was a fulfillment to Abraham.
The reason that we need God is because it is through a Christian life that we are actually blessed.
Someone might think that their life is good enough without God. But nobody is actually pursuing moral perfection without God, and while life may certainly be enjoyable, it is not in the process of truly being bettered without a relationship with God.
This ties into something else... There are two ways in which a man or woman should live. One is as a member of his family. Obeying one's father & mother is an extremely fundamental order, and a testament to the importance of family in the classic world.
The other way is to be as Christ -- indeed, one of the things that led me from Protestantism was the utter lack of "Eunuchs for the Kingdom," even though it says right in the Bible the following:
For there are some eunuchs, which were so born from their mother's womb: and there are some eunuchs, which were made eunuchs of men: and there be eunuchs, which have made themselves eunuchs for the kingdom of heaven's sake. He that is able to receive it, let him receive it. Matthew 19:12
What is a Church if it does not actually have a place reserved for the celibate man who works for the Kingdom? What is a Church that is alien to this tradition? It does not properly connect even with the words of our Lord & Savior. But that is not quite the point of this OP...
The point is that one should either be a mother or father, living one's life productively within their family or they should be a monk or nun for God.
I've known many men and women who returned to religion through having children. The whole experience is overwhelming and it is like gaining a third eye through which one sees the world differently, and one feels a more profound connection. It is as Ryan Landry frequently stated... You suddenly have skin in the game. You suddenly care about things in a way that you never cared before.
It is important to know that while life can be adequate and enjoyable without God, no single person can begin to provide a structure that is sufficient in an ultimate form.
That is to say... man is incapable of transcending himself and being blessed in the most profound ways outside of Christ, and if he fails to give Christ to his children (and his family) he has not properly fulfilled a sort of existential debt. He has only pulled others into the mediocrity of existence and, indeed, should he bear fruit that is clinically depressed or handicapped, he would not be mistaken to think that he may have only brought rote suffering unto a life without an egress.
Christ is the blessing that gives meaning in all things.
We need God to enjoy this blessing. And, without it, while life can be enjoyable for an individual, while life can even be enjoyed as a family unit, there is the Sword of Damocles hanging over your head. To enjoy things and to be surrounded by a family but to not know, and to be purposeless.
WIth God, we are blessed, and there is a path that one walks and a goal towards one moves. There is context and purpose beyond the self, and when this exists there is an actual blessed status.
Without God there is only existential uncertainty and whatever purpose the weak and dark mind of a man can conjure up.