Disclaimer:
I was raised Christian Catholic but I always thought it sucked (except a superstitious bout when I was a teenager under the influence of the Hale-Bopp comet.)
It is not my intention to ridicule religion. But if you think I am making fun of you or of your religion, and you think you must do justice to it, then there is something wrong with your faith, which should not be shaken so easily.
My knowledge of other religions is very limited.
I also do not put detailled bibliographical references; while I am sure that I picked up the concepts below from plenty of books I chaotically and mindlessly read, since I am talking about beliefs I find it ridiculous to support my reasonings on belief with ad auctoritatem arguments.
Take what you see below as the velleity of a late adult with lots of time available.
Anyway, most of the thoughts here surely emerged thanks to this book by the good old Alan Watts: Myth and Ritual in Christianity, Thames and Hudson, ISBN 0-8070-1375-7
Man's woes ride on uncertainty; certainty is where desperation dwells.
Which is my personal rephrasing of the much more effective
[...] wee lie down in a hope, that we shall rise the stronger; and we lie downe in a knowledge, that wee may rise no more." (John Donne)
I think there are two main themes at work in Christianity.
The perception of time seems to me the feature that distinguishes the two themes.
In 'Without': Time is absolute. The self, being the vehicle to travel through it, is the same throughout life; or at least it is responsible for its history, its previous thoughts and deeds will be taken into account at the end of time to decide salvation.
In 'Within': Time is limited to the time the individual is alive, or to this very moment we call 'present'. The self is under constant transformation. Each moment is an apocalypse; each moment can deliver salvation (that is, end of angst). After death there is no after, or rather: it does not matter for salvation, as salvation is being one in God and can happen in time, any time. What man experiences as the time passing is part of his being alive; concepts arising from our social nature -- personality, for instance -- are non-material aspects of reality, so as the color of our hair is a material aspect of reality.
The 'Without' theme is surely the one ordinary Westerners can better comprehend and think of when talking about Christianity. This is due of course to the great influence this interpretation of religion exerted in the past and still does in most of the entertainment media (because, frankly, thinking about these topics is entertainment in the broadest sense).
Recall that these interpretations concretize God as an old wise man, the Son as a young man sometimes portrayed as suffering, crucified, the Holy ghost as a dove. It is very easy to confuse the symbol with what it actually represents, and this in my opinion is what happens with the 'Without' theme. There is an old man, his son and a bird waiting at the end of your life, with a scale.
I think the 'Without' theme is what prevents most people from enjoying their lives. When caring more for the 'Without' than the 'Within', man tries to find a framework of though to explain what there is, what it will be, what it needs to do, what he must not do. This is because he does not know what will happen next. But this is the natural condition of man.
I may be far-fetching, but in my opinion this attitude is what prompted man to develop science as a way to predict the future. Ancient Romans seem to have had this attitude: we sacrificed 10 goats to Mars, we won the war; next war let's make sure we do the same. But the tool to make this conjuring work, the experiment, applies only under certain conditions, which do not apply in answering questions about the meaning of an individual's life (and are not met nor looked for in the above example).
Science is the first validation-based, explicit framework for predicting the future that works.
Superstition is not validation-based; but it is an explicit framework too to predict the future. In this respect, the 'Without' theme counts as superstition. Ex-voto are the 10 goats I mentioned before, translated in the catholic world.
Being certain per se does not deliver from pain; a man being tortured might not be happy with his imminent certainty.
The certainty one looks for is that something good is going to happen, not that nothing or something bad will happen.
Certainty of Paradise makes afterlife sweeter, but the uncertainty of being on the right track makes life bitter. Uncertainty of certainty, or vice versa, condemns to a lifelong storm.
The 'Within' is, in my opinion, a much more relieving way of seeing, because it gives up fighting the uncertainty, and embraces the certainty that salvation is at hand.
Since time is relative in this view, the existence of the historical Jesus Christ is not even an issue for the religious person. Father, son and holy ghost represent this becoming.
It is harder to fool oneself to believe in a god with a scale, since there is no final judgement; life is whatever needs to be; God is everything, but each thing is not God; rather, there is God in every thing. God is the term one uses to express the things being, which seem to defy definition; a colorful metaphor would be that of a baroque fountain, in which water flows and creates patterns; the world is the fountain, the water flowing in it is God; the fountain takes life and is pleasant because of what can be appreciated while happening. I understood that this is more or less the way the philosopher Baruch Spinoza conceived God.
The 'love' of God is not the one suggested by taking literally the old man with scale metaphor. Rather, 'love', which is God, is the things as they are; and being in harmony with them (the atonement) is salvation.
Do not read this as promoting passivity. Even when forcing things to our will, which by necessity will happen, being in harmony with such love means that the event of failure, in the eternal 'now', has been contemplated. Uncertainty of certainty, or vice versa, saves from wrecking in grief.
Uncertainty rocks man's will, awake; grief falls asleep in certainty.