Kierkegaard has an interesting view on this.
He states that man is in a relation to a particular object, he can view the "truth-hood" of this particular object through an objective or subjective lens. In the case of the former, the object's truth in-and-of-itself is examined. This would be like a person knowing that Socrates bought apples yesterday because he said he would and Socrates never lies.
Subjective truth is concerned with the relationship between object and the viewer of that particular object. This would kind of be like examining the apple and knowing it is real through the sound it makes as you bite into it, the taste of it as you chew it in your mouth, and the satisfaction you might feel once you have finished your snack.
Kierkegaard argues that each of these positions, by themselves, is undesirable. Objectivism, when pondering the truth of God, would require a set of proofs and premises that would need to be flawless, as a minor argument's falsehood could crumble the proof one might have constructed for this divine being. Subjectivity is not necessarily better -- it could potentially lead someone to believe something is true that might not exist at all.
It is clear that man is a synthesis of subjectivity and objectivity, but this synthesis is not in a state of finality. His fixed nature (genetics, perceptions and limitations of others, situation) shall always be in conflict with his infinite nature (the part of man that can create, develop, change, and transcend). Therefore, there is only one authentic way to believe in God. A believer must be in the state of passion that arises when subjectively believing in a God, while realizing that His existence is a potential objective falsehood.
I know that wasn't very eloquent, but I hope I did an okay job of reciting a general idea of Kierkegaard's beliefs. Any other existentialism enthusiasts should feel free to correct me if I failed to explain a point clearly.