Luke 22:20

Likewise also the cup after supper, saying, This (g) cup [is] (h) the new testament in my blood, which is shed for you.

(g) Here is a double use of metonymy: for first, the vessel is taken for that which is contained in the vessel, as the cup is spoken of for the wine which is within the cup. Second, the wine is called the covenant or testament, whereas in reality it is but the sign of the testament, or rather of the blood of Christ by which the testament was made: neither is it a vain sign, although it is not the same as the thing that it represents.

(h) This word "the" shows the excellency of the testament, and corresponds to (Jeremiah 31:31) where the new testament is promised.