"What should we conclude?" Paul asks this question to move his reader to his next point. You can translate this as a statement. AT: "This is what we need to remember" (See: [[rc://en/ta/man/translate/figs-rquestion]])
This is a metaphor about the fact that the people are spiritually dull. They are not able to hear or receive spiritual truth. (See: [[rc://en/ta/man/translate/figs-metaphor]])