Difference between Knowing and Understanding.
It is important, however, to bear in mind the difference between knowing and understanding, or comprehending. A child knows what the words “God is a spirit” mean. No created being can comprehend the Almight unto perfection. We must know the plan of salvation; but no one can comprehend its mysteries. This distinction is recognized in every department. Men know unspeakably more than they understand. We know that plants grow; that the will controls our voluntary muscles; that Jesus Christ is God and man in two distinct natures, and one person forever; but here as everywhere we are surrounded by the incomprehensible. We can rationally believe that a things is, without knowing how or why it is. It is enough for the true dignity of man as a rational creature, that he is not called upon by his Creator to believe without knowledge, to receive as true propositions which convey no meaning to the mind. This would be not only irrational, but impossible.
Charles Hodge Systematic Theology. Vol 1, III.5.A (p.50)
B. Reason must judge of the Credibility of a Revelation.
.. A thing may be strange, unaccountable, unintelligible, and yet perfectly credible. What is strange or unaccountable to one mind, may be perfectly familiar and plain to another. For the most limited intellect or experience to make itself the standard of the possible and true, would be as absurd as a man’s making his visible horizon the limit of space. Unless a man is willing to believe the incomprehensible, he can believe nothing, and must dwell forever in outer darkness. The most sceptical form of modern philosophy, which reduces faith and knowledge to a minimum, teaches that the incomprehensible is all we know, namely, that force is, and that it is persistent. It is most unreasonable, therefore, to urge as an objection to Christianity that it demands faith in the incomprehensible.
Ibid., Vol.1 III.5.B (p.50)
DFR 