Here Paul switches to a direct, personal appeal, using the singular form of the pronoun you.
From this form of address (and from the absence of any direct rebukes, as can be found in 1 Corinthians 5:1 – 6:20), it seems that his argument is most likely hypothetical. Church members have not actually gone ahead and eaten sacrificial food (for further support of this conclusion, see 1 Corinthians 11:2). However, they were questioning the legitimacy of this prohibition (especially given their knowledge that there is only one God).
Paul’s question contains an ironic reference to his earlier statement that love builds up
(1 Corinthians 8:1). Literally, he asks if a fellow believer would not be built up
(encouraged
) to eat food offered to idols if he sees his brother doing it!
10 For if anyone sees you who have knowledge eating in an idol’s temple, will he not be encouraged, if his conscience is weak, to eat food offered to idols?