I agree that in philosophy and in logic the appearance of a thing is not a proof of the thing itself. But can the same be said in theology?
If God made the universe and made us in it, why would he not want us to experience it as it is? Why would the appearance of things not be the best guide to what the thing in itself is? I don't mean to identify appearance of reality with reality, but if appearance--well-tested and corroborated by multiple observers and through multiple tests--is not a reliable guide to what God created----then what is?
What else do we have to display the power and glory of God to us than the creation as it appears to us?
Theologically creation reveals only the power, wisdom and artistry of God. It took the person of Christ who dwelt amongst us to reveal the full extent and richness of Gods love, mercy and grace. The appearance of the thing in itself before this revelation was incomplete and left kings and honest men longing to know more. After this revelation all that was said before needs reappraisal.
Just as man , the created creature, images in a small way his Creator the understanding of God gives us concepts with which we can approach creation itself.
1) God is one and God is three - so also there is an integrity and a diversity to creation.
2) Jesus is the miraculous Almighty one through whom all things were made but so also he is the finite, fragile creature with the limited experience of a short life on planet Earth. If we focus on the Divine we see a universe which God could have created with a click of his fingers never mind 6 days. If we focus on the humanity we have speculative theories that attempt to explain on the basis of our limited experience of what God has created.
3) In the world of the OT the Jews read the political messiah prophecies with great enthusiasm and missed the ones about a Saviour who would dwell with them in humility and ultimately make the supreme sacrifice for them. So when their messiah came they did not recognise Him.
When we assess the appearance of a thing and attempt to understand its reality we can get it terribly wrong for a great many reasons.
1) We can overstress the consistenty of our theories and miss the diversity that these theories must also accomodate.
2) We can attribute divine certainty to what is merely human speculation.
3) We can read what we want to read and miss the thing that does not fit our values and which may actually overthrow our theories.
The overthrow of Ptolemy by Galilleo and Copernicus was a monumental shift from what had seemed apparent for so long to a deeper perception of the reality itself. But still the search continues - reality is not yet even within our grasp when we speak of the stars we only have the appearance of the thing and better and better theories about it. Some of these theories may well be completely off the mark.
I am reading a load of stuff about what it means to see, the effects of distortions (like the stick in water) and after images and mirror images for instance distort our perception of what is real. Across the gulf of the stars our vision cannot afford the philosophical distortions that we bring to the act of seeing. We see so little of and we see so imprecisely what is out there and have so little time to digest what we see. So when we do see a thing we need to be sure that we can trust what we see and see it as it is. Until we see we are only blind men staring into darkness seeing the occasional dots and flashes.