Why does Bertie ask Jeeves for a strengthening drink in Chapter 1?

In Chapter 1, when Jeeves returns from holiday, Bertie asks him to make him a drink, noting that Jeeves' drinks are capable of strengthening a man. Bertie needs strength because when the two men are finally in the same room together, Jeeves sees that Bertie has grown a moustache in his absence. Jeeves disapproves of the moustache and Bertie, given courage by the drink, defends it.