Biblical Understanding based on the Record of Scripture
The Passover Israel observed on the 15th in the Old Testament was the same Passover Jesus continued to observe on the 15th throughout His lifetime. Jesus did fulfill the sacrifice of the lamb on the 14th but He never changed the observance of the 15th to that same day. The disciples, accordingly, continued to observe the Passover at the beginning of the Feast of Unleavened Bread just as Jesus did and as their fathers had before Him.
