Biblical Christians believe the Bible to be truth. So when asked what the truth is, as you have stated, we use scripture. The other reason (speaking for myself) I do this is because when I quote the Bible I am speaking upon the authority of His Word. If I were to give you my own thoughts and perspectives I come upon my own authority. If you are looking for something outside of scripture to prove the inherrancy of scripture (or a proof that God exists) one still has to look to scripture to discuss it. That being said from a non-biblical theist perspective (and not using scripture) I would say that creation (namely the earth and all the plants, animals, people, etc) is my evidence for the existence of God. I realize atheists reject creation because it speaks to a creator and they don't believe in one. So the natural question then arises: Where did we come from? If we were created then we believe in a creator. If we don't believe in a creator we look for another explanation. I will only discuss evolution here because it seems to be the most widely held argument in opposition to creation and thus God. I will define evolution as chance through time. Evolution seeks to prove that through time (millions of years), and chance (things just happened to come together in just the right manner) life was created and then evolved and humans are the most recent of that evolution.
My evidence through creation is that God has given the creation as an evidence/witness for Himself. As an analogy: you look through a telescope at the moon. You see the American Flag on a pole stuck into the moon's surface. What is the more likely scenario; that the flag got there by chance through time, that it just happed (evolution) or that someone put it there (creation). Similarly the empire state building. I didn't physically observe anyone design and build this building. Yet I believe it was created and built by an intelligent designer (creation), and the building itself bears witness to it's designer/creator. (much like the mayan ruins and Egyptian Pyramids bear witness to previous civilizations). I do not believe that the building got there by chance through time (evolution).
So scripture aside, there are and have been people who have held to the view of creation that reject the Biblical account of it. And as such they believe in a creator but not the one spoken of in the Bible.
My evidence through creation is that God has given the creation as an evidence/witness for Himself. As an analogy: you look through a telescope at the moon. You see the American Flag on a pole stuck into the moon's surface. What is the more likely scenario; that the flag got there by chance through time, that it just happed (evolution) or that someone put it there (creation). Similarly the empire state building. I didn't physically observe anyone design and build this building. Yet I believe it was created and built by an intelligent designer (creation), and the building itself bears witness to it's designer/creator. (much like the mayan ruins and Egyptian Pyramids bear witness to previous civilizations). I do not believe that the building got there by chance through time (evolution).
So scripture aside, there are and have been people who have held to the view of creation that reject the Biblical account of it. And as such they believe in a creator but not the one spoken of in the Bible.