Old Testament scripture is spoken of as if it were a person who could encourage others. Alternate translation: "what God has instructed you in the scriptures to encourage you" (See: [[rc://en/ta/man/translate/figs-personification]])
The word translated "sons" and "son" is specifically the word for a male child. In that culture the family line continued through the sons, not normally through the daughters. (See: [[rc://en/ta/man/translate/figs-gendernotations]])
This can be stated in positive form. Alternate translation: "take it very seriously when the Lord disciplines you, and do not grow weary" (See: [[rc://en/ta/man/translate/figs-litotes]])