^a Gk. ἐν τῷ κρυπτῷ, in the secret (thing) (contra ἐν τῇ κρύπτῃ, in the crypt or cellar). Usually translated in secret or in private; however, one would then expect ἐν κρυπτῷ. Outside Mt. 6:4, 6, and 18, the expression ἐν τῷ κρυπτοῷ is only found in Rom. 2:29 in ὁ ἐν τῷ κρυπτῷ Ἰουδαῖος, translated inwardly a Jew (opposite ὁ ἐν τῷ φανερῷ Ἰουδαῖός in Rom. 2:28, translated outwardly a Jew). Likewise, in Mt. 6 the meaning seems more likely not to be to make an effort to hide something; but perhaps rather to not overtly show it, i.e., covertly; idiomatically equivalent to: behind the scenes; behind closed doors; out of sight; out of view; out of the public eye; in the background. Even in 6:3, the instruction to not let know can be construed as not to conceal what the right hand is doing from the left hand, but to not announce it or make a show of it to the left hand.

^b Gk. ὁ πατήρ σου ὁ βλέπων ἐν τῷ κρυπτῷ, your father who sees in the secret (thing). See also Gk. Dn. 13:42 [Susanna 1:42]: ὁ θεὸς ὁ αἰώνιος ὁ τῶν κρυπτῶν γνώστης, the eternal God who knows the secrets (referring to schemes of men against Susanna and the truth behind their false testimony).