Catechesis: Both Kinds

The laity are given both kinds in the Sacrament of the Lord’s Supper because this practice has the Lord’s command, ‘Drink of it, all of you.’ Christ has clearly commanded that all should drink from the cup.—AC XXII:1, 2 

*This is directed against the Roman prohibition (at the time) of the cup to the laity; it is not without import for modern deviations from the institution either.