Mat 6:18 That you do not appear to men to fast, but to your Father who is in secret: and your Father, who sees in secret, shall reward you openly.

This is an extremely revealing verse, saying something that is almost never said about God, that He is hidden.

"Appear" is phainô, which means "to bring to light," "to shine," "to cause to appear," and "to shine."

"Secret" is kruptos, which means "hidden," "concealed," "in disguise," and "secret."

"Openingly" is en (in) phaneros, which means "visible," "open," "conspicuous," "illustrious," and "manifest."

A little earlier, Christ said that the Father was "in heaven." Here he uses as similar phrase to say "the Father in hiding" or "the Father in secret."

He uses his frequent equation balancing the social and the spiritual. You have to choose whether you want to make yourself "shine" before men or keep your sacrifice hidden before men so God that God will make you shine.