Moses continues comparing the enemies of the people of Israel to grapevines that produce poisonous fruit and wine. This means their enemies are wicked. (See: [[rc://en/ta/man/translate/figs-metaphor]])
This question emphasizes that Yahweh's plans for the people of Israel are kept secret like a valuable treasure. The rhetorical question can be translated as a statement. It can also be stated in active form. AT: "I know what I have planned to do to the Israelite people and to their enemies, and I have locked up those plans as someone would lock up his valuable possessions." (See: [[rc://en/ta/man/translate/figs-rquestion]] and [[rc://en/ta/man/translate/figs-activepassive]])