“Metaphysics and epistemology are correlative; the nature of God determines His knowability” (Frame, The Doctrine of the Knowledge of God, 19). Part of what may constitute “evidence” for a proposition depends upon the nature of the proposition.
Let us say we wish to determine whether X is a good baseball player. X’s preference for a flavor of ice cream does nothing to reveal his skill at baseball. If wish to look for evidence of a bird, a compass will likely provide no useful information.
When it comes to the matter of God’s existence, the nature of evidence will correlate to the nature of God. Thus, when someone accepts or denies “evidence” concerning God they have already committed to a certain concept of God.
For example, one a particular day it rains. One person denies that such rain could possibly provide any evidence of God’s existence. Fair enough. But, what should it look like if God were to make it rain? Would rain only be evidence of God if it were to occur contrary to the “normal course” of events? You see, the god or God found or denied depend upon one’s presuppositions. (Now, those presuppositions are subject to interaction with perception. However, perception does not occur in a “neutral” space. )
(John Piper has a delightful meditation on how rain shows evidence of God — and should be a profound ground for our thankfulness. http://www.desiringgod.org/resource-library/taste-see-articles/the-great-work-of-god-rain)
When someone denies the physical world provides any evidence of God, that person is denying God’s existence but rather denies a god who the denier presumes to existence.
Let us say you meet someone at college — a new classmate. Your classmate claims to have a girlfriend — but the girlfriend lives in his hometown. You deny the girlfriend’s existence and say, “If she were your girlfriend, she would live here. Therefore, since this woman is not here, she is not your girlfriend.”
When one denies God’s existence on the ground that the universe is regular in its operation, one has not denied the God asserted in the Bible. The God of the Bible provides order and law. The God of the Bible is Lord of all creation and thus orders and controls the physical universe “without losing His divinity” (Frame, 20).
Frame explains that the God the Bible, the Lord of creation does not merely control the universe, He also has authority over the creation. Therefore, all valuations of the universe necessarily entail God’s existence.
Moreover, God is present [the third aspect of lordship identified by Frame] in the universe (as a third aspect of being Lord). Therefore, “all reality reveals God” (Frame, 20). “God is unavoidably close to His creation. We are involved with Him all the time” (Frame, 17).
Thus, “The agnostic argument, …presupposes a non-biblical concept of God. If God is who Scripture says He is, there are no barriers to knowing Him” (Frame, 20).