Is there a God, part two: Why are we even here?
Christians currently find ourselves in concurrence with the prevailing scientific view, that the universe had a beginning. Science can say little more, as the laws of nature break down in the singularity from which the Big Bang occurred.
At this point, we could shrug and mumble that the universe must have somehow created itself, or we could say that maybe there is an unknown eternal entity, an uncreated creator, that brought it into being. Christianity shouts "yes" to option 2. Until the enlightenment, nearly all reasonable scholars would have agreed, based purely on logic; In option 1, in order for something to create itself, it would have to exist prior to existing, which is a logical impossibility.
An uncreated, eternal being may be mysterious and difficult to imagine but it is not inherently illogical. An entity that creates itself is not merely a mystery, or a paradox, but an impossibility, unless we are willing to throw out logic. If you throw out logic, then you destroy the foundations of science and reason altogether. You can live live without reason, but good luck to you.
Now, a creative eternal entity need not be the same thing as "God", the way religious groups define such a being. We could stop right there at a "necessary being", and many philosophers throughout history have done just that. In the 18th century, this prevailing idea was called "deism." The creator of all things was viewed as a cold and aloof architect of the universe, who started things up and then went away, and did not intervene any further.
Before leaving this topic, I might suggest that we can surmise a few things about an entity that is eternal and able to create our universe. Such a being of course is "transcendent" by definition--that is, the entity is "outside" or "beyond" the confines of this universe. You might get also some ideas about this sort of endeavor needing an unimaginably vast intelligence and immense power, and these ideas match up well with the Christian (as well as Jewish and Muslim) ideas of God. The Christian believes in a God that is eternal, transcendent, all powerful and all knowing. A term often ascribed to this view is "theism"
(See also the topic Does God Exist?. This page contains a bibliography of useful resources).