[ He has to bristle at the invitation to "want" to teach him. As though he wants to "teach" anyone magic. What he wants is far beyond this place, far beyond this little prison cell with its dingy cot and worn walls. He wants to go home. Not babysit some worthless hostage.

Emet-Selch sighs. ]

Your dedication to magic has proved wanting in the past, but there is no doubting your dedication to this cause, at any rate.

I will teach you for two weeks. If you manage to show enough dedication to show up for an entire fortnight without fail, then I will give you lessons as long as seems necessary.

[ In other words: prove his dedication to wanting lessons. Yes, he had offered them to the group at large, but that still does not mean he does so without some scrutiny. ]