respectful, sincerely
愨 centers on a sincere, respectful inner attitude: being earnest and reverent in one's conduct.
愨 combines 殻 (or a related phonetic element) with 心 (heart), suggesting a sincere, respectful heart. The exact historical development is uncertain.
The bottom 心 (heart) is the key: picture a heart wrapped in a protective shell (the upper part), keeping it sincere and respectful.
For カク, imagine a respectful person giving a firm 'knock' (カク) before entering, showing sincere reverence.