So far as I can tell, he means no harm to you now, yet there is...another interest which worries me still. However, when a Servant is summoned, the Master is given something called a Command Spell, several of them. The use of which forces the Servant to do exactly as the Master bids, consequently, having one at all keeps a Servant in line, for fear of its use. Because you have not summoned me, and because the Grail is not here, even my Master has none. But I believe an artificial seal could be made, or at the least, something very similar. For you.