Last Supper and Garden Prayer
The Passover lambs were killed (Mark 14:12) on 14 Nisan (Mar./Apr.). That evening, the Passover meal was eaten. The Feast of Unleavened Bread followed immediately after Passover, from 15–21 Nisan. The entire time was often referred to either as “Passover” (Luke 22:1), or as the Feast of Unleavened Bread. Therefore the first day refers to 14 Nisan.