One could point to the importance of the Image of God in humanity. Being made in God's image means every individual person has an inherent dignity and worth. Also the necessity of personal faith to show the importance of the individual. Personal faith imply the centrality of the individual. Converts are made voluntarily without cohesion and thus since conversion is individualistic the religion is as well.
On the other side, Christian theology also teaches that individuals are "saved" by being (to use Paul's language) "in Christ", a collective concept. Jesus died for a people, the people of God, the new humanity "in Christ" (Eph 2). This means that the convert is now numbered among the redeem, made a part of the whole, body of Christ, the church (1 Cor 11-12).
So where should a Christian begin thinking about social issues? What is the proper starting point for a biblical social theory? How do we construct a Christian view of political realities? A fundamental category needed to answer those questions is the primacy of the individual or the collective. Should Christian begin from the point of the individual or from the group? Should we think of goods in terms of the whole or of its parts? Two giants in Christian thought weigh in on the issue: J. Gresham Machen and C.S. Lewis. I will gives Machen's answer then Lewis. Quick note on Machen – the ‘liberalism’ he is speaking of is not the current, progressive liberalism, but rather the theological liberalism of the early 20th Century. [1]
"It is true that historic Christianity is in conflict at many points with the collectivism of the present day; it does emphasize, against the claims of society, the worth of the individual soul. It provides for the individual a refuge from all the fluctuating currents of human opinion, a secret place of meditation where a man can come alone into the presence of God. It does give a man courage to stand, if need be, against the world; it resolutely refuses to make of the individual a mere means to an end, a mere element in the composition of society. It rejects altogether any means of salvation which deals with men in a mass; it brings the individual face to face with his God. In that sense, it is true that Christianity is individualistic and not social.
But though Christianity is individualistic, it is not only individualistic. It provides fully for the social needs of man. In the first place, even the communion of the individual man with God is not really individualistic, but social. A man is not isolated when he is in communion with God; he can be regarded as isolated only by one who has forgotten the real existence of the supreme Person. Here again, as at many other places, the line of cleavage between liberalism and Christianity really reduces to a profound difference in the conception of God. Christianity is earnestly theistic; liberalism is at best but half-heartedly so. If a man once comes to believe in a personal God, then the wow ship of Him will not be regarded as selfish isolation, but as the chief end of man. That does not mean that on the Christian view the worship of God is ever to be carried on to the neglect of service rendered to one’s fellow-men − ”he that loveth not his brother whom he hath seen, is not able to love God whom he hath not seen” − but it does mean that the worship of God has a value of its own. Very different is the prevailing doctrine of modern liberalism. According to Christian belief, man exists for the sake of God; according to the liberal Church, in practice if not in theory, God exists for the sake of man. But the social element in Christianity is found not only in communion between man and God, but also in communion between man and man. Such communion appears even in institutions which are not specifically Christian."
- J. Gresham Machen, Christianity and Liberalism, pg. 137-138
Now batting clean-up, C.S. Lewis on the twin errors of ‘Totalitarianism’ (Collectivism) and individualism:
"The idea that the whole human race is, in a sense, one thing —one huge organism, like a tree—must not be confused with the idea that individual differences do not matter or that real people, Tom and Nobby and Kate, are somehow less important than collective things like classes, races, and so forth.
Indeed the two ideas are opposites. Things which are parts of a single organism may be very different from one another: things which are not, may be very alike. Six pennies are quite separate and very alike: my nose and my lungs are very different but they are only alive at all because they are parts of my body and share its common life. Christianity thinks of human individuals not as mere members of a group or items in a list, but as organs in a body—different from one another and each contributing what no other could. When you find yourself wanting to turn your children, or pupils, or even your neighbors, into people exactly like yourself, remember that God probably never meant them to be that. You and they are different organs, intended to do different things.
On the other hand, when you are tempted not to bother about someone else’s troubles because they are “no business of yours,” remember that though he is different from you he is part of the same organism as you. If you forget that he belongs to the same organism as yourself you will become an Individualist. If you forget that he is a different organ from you, if you want to suppress differences and make people all alike, you will become a Totalitarian. But a Christian must not be either a Totalitarian or an Individualist.
I feel a strong desire to tell you—and I expect you feel a strong desire to tell me—which of these two errors is the worse. That is the devil getting at us. He always sends errors into the world in pairs—pairs of opposites. And he always encourages us to spend a lot of time thinking which is the worse. You see why, of course? He relies on your extra dislike of the one error to draw you gradually into the opposite one. But do not let us be fooled. We have to keep our eyes on the goal and go straight through between both errors. We have no other concern than that with either of them."
-C.S. Lewis, Mere Christianity, Bk. 4, pg. 6
So, is Christianity collectivistic or individualistic? The two quotes above point to a more both/And answer. The theological starting point that best captures what Machen and Lewis where getting at is the Christian God. So A Christ followers reflection on social theory is God, the distinctly Christian God, revealed in the doctrine of the Trinity. The Trinitarian God of Christian faith gives us the proper categories for understanding a well ordered society
Only the Trinity can act as a guide for thinking about political realities. It protects from diminishing the value of the individual or the obligation to the common good. The doctrine of the Trinity as a starting point for reflection on social realities helps to join apparent unbridgeable opposites. Who said doctrine is dry and not relevant to current issues? Our God gives us a vision of how the individual and the many can be one. The analogy is helpful but not without flaws. It does brake down down at some point, a community can't be one as God is one. Yet the doctrine of the Trinity gives us a way to balance the tension between collectivism and individualism. I think that a beautiful beginning.
Footnote
[1] A precursor to the modern progressive movement, rooted more in enlightenment epistemology than postmodern thought thus different in many ways but none the less progressive for its day.