The Savior answered and said,
"If what can be seen is obscure to you, how can you comprehend what cannot be seen?
If deeds of truth that are visible to the world are hard for you to accomplish,
than how can you accomplish things that are invisible,
things concerned with the exalted greatness and fullness? ..."



Jesus is telling Thomas that he must understand earthly matters before he can truly comprehend Heavenly matters,
and he must teach what he knows to others if he wants to advance spiritually.